How to exceed ram limit?
According to Mactracker, your MacBook 13-inch, Early 2009 (A1181, early 2009) can handle 6 GB RAM, or 2 GB more than Apple's 4 GB spec. You'd need to use a combination of a 4 GB and 2 GB 200-pin PC2-5300 (667MHz) DDR2 SO-DIMM.

See also: Apple MacBook "Core 2 Duo" 2.0 13" (White-09) Specs at EveryMac.com