How do airports determine when they should change their runway numbers?
Implementing changes to runway numbers is quite complicated and requires a lot of different parties to get involved.  There is a ton of related information in FAA Order 8260.19E and it has the details.
Simple Version
According to an article by the NBAA called &quot;How Changes in Magnetic North Are Impacting Airports&quot;:

“Adjustments to runways like this and to navigational aids are
ongoing,” according the Kathleen Bergen, a spokeswoman for the FAA
Southern Region. “Every five years, the FAA reevaluates shifts in the
pole—its magnetic variation—and makes changes to runways and flight
procedures as needed,” she said.

Medium Version
NOAA, NOS, and NGS (see below) provide the magnetic variation information, and publish it every five years.  They work with a bunch of different offices, and different branches of the military as they make adjustments.  When a determination is made that a runway number should be changed, they coordinate with several other groups (such as AeroNav Products, OSG-FPT, the applicable Airportt Traffic Service Area Office, and the Airports Division), to choose the actual number used, based on &quot;careful consideration and evaluation of a number of factors&quot; and then to make the actual changes in charting, runway markings and signs, etc.
They are supposed to change it when it is more than three degrees off from what it is should to be.  AC 150/5340-1L - Standards for Airport Markings contains the official runway designator rules (paraphrased):  If the actual magnetic course of the runway ends in 5, it can use either number, otherwise you round to the closest runway number (there are some variations for special cases like parallel runways and such, but this covers most runways). So in your example, 145 is still valid as runway 14, and they wouldn't need to change it until it exceeds 148 deg.  In your case, the annual rate of change for Farmingdale airport (as of 2010) is 0.0 deg East, so I don't see that happening for awhile.
Long Version - Quotes from FAA Order 8260.19E (above)

Section 5. Implementing Epoch Year Magnetic Variation (MV)
a. Background. The National Oceanic and Atmospheric Administration
(NOAA), National Ocean Service (NOS), and the National Geodetic
Survey (NGS), for all areas of the United States and its territories
for application to navigation charts and maps, is the source for
magnetic variation (MV) information and tools for establishing
magnetic variation. Changing values for MV are tabulated and published on
a 5-year epoch basis; e.g., 00, 05, 10, 15, 20, etc. In order to
assist in stabilizing the National Airspace System (NAS), a fixed
value of MV is assigned to each  navigational aid and airport as the
Magnetic Variation of Record. This value is applied to true
directions to obtain the magnetic values for radials, courses,
bearings, and headings published in instrument flight procedures.
Periodic updating of the MV assigned to navigation facilities is
required to maintain reasonable proximity of alignment with the
earth’s ever-changing magnetic field. ...
b.
Participating Offices. Management and control of Epoch Year MV values
require action  by the following offices:
(1) AeroNav Products.
(2) Military Organizations.
(3) National Flight Data Center (NFDC).
(4) Western, Central, and Eastern Technical Operations.
(5) Western, Central, and Eastern OSG-FPTs.
(6) Regional Airports Divisions.
...
f. Regional Airports Division/Airports District Office (ADO).
Coordinate with the  applicable OSG-FPT prior to establishing or
revising runway designator numbers for an airport  having one or more
instrument approach or departure procedures, to determine the
appropriate MV to be applied to the runway true bearing. Determination
of the runway designator number should be a matter of joint agreement
with AeroNav Products, and be accomplished sufficiently in advance to
allow for procedural amendments. Take appropriate NOTAM action if
repainting of an affected runway has not been accomplished on the
required date.
...
2-18. Guidelines. The identification and selection of navigational
aids or airports as candidates for revision of MV of Record require
careful consideration and evaluation of a number of factors - as the
impact of MV changes can be considerable. The applicable Air Traffic
Service Area Office may have to initiate or revise published air
traffic procedures; the Technical Operations Service (AJW-0) is
directly involved in facility rotations and requires proper
coordination. The Airports Division, or appropriate military
authority, may have to arrange for repainting of runway designator
numbers [see paragraph 8-58e(2)(e)].
a. MV versus Epoch Year Value. When the difference between the MV of
Record and the nearest future Epoch Year value of any navigational aid
or airport is 3 degrees or more, the MV of Record must be changed to
the nearest future Epoch Year value.