How do you find out what changes there are in new firmware?
Firmware update
A firmware update usually brings to your device bug fixes or new features. This is good because insures your device security and readiness for a stable usage.

After spending one hour trying to find a changelog for Samsung firmwares, the best I could came up with was this website:
SamFirmware

What is this? The firmware page of SamMobile is specially for the die-hard Samsung owner.

Since firmware are country related, and I don't know yours, you can try to locate the firmware there:
Your new version:

PDA:LPD / PHONE:LPB / CSC:LPD (TMU)

Marked at bold what's relevant to find that firmware.
Enter LPD in the search box and look at the column &quot;CSC&quot;, than locate the row with the firmware released for your country.
Note: Nonetheless, there's not much information available.

There's also:
This two websites provide a comprehensive list of the firmwares released:

Samsung Galaxy S2 Firmware Updates via Kies Official Releases compiled list

How To Update Samsung I9100 Galaxy S II Firmware



Locate your current firmware

Touch Menu;

Touch Settings;

Scroll to and touch About phone;

The software version will be displayed.