Vostro should have 2 個 SODIMM 插槽, support DDR3,1333 MHz 1 GB / 2 GB / 4 GB (according to the manual)
To check the compatibility, better use CPU-Z (http://www.cpuid.com/softwares/cpu-z.html) to check the speed/ car latency of existing RAM (CL-?), then purchase a new one with the same timing (e.g. 9-9-9-25). But in case the timing NOT exactly match, it should be no problem but with lower speed (of course depends on what RAM). Suggest to have kingston with better compatibility (~180 for DDR3-1333 4G SODIMM)