The amount of RAM you can fit will be limited by the number of SO-DIMM sockets and their capacity.
Most laptops only have two sockets - Older (refurbished) laptops will not support the higher capacity Sodimms 2 x 16Gb = max 32Gb what ever laptop you look at check the max memory capacity you may find you are limited to a max of 8Gb.
Memory sped is another factor
DDR2 SO-DIMM memory modules commonly have clock speeds from 200 MHz up to 800 MHz PC2-6400.
The latest 204-pin SO-DIMMs can contain DDR3 SDRAM, with specifications such as PC3-6400, PC3-8500, PC3-10600, and PC3-12800.
The way I do it is to find one that looks like what I need, such as this one say, and then search for its specifications. This is the spec, click here and it says there
"Supports up to 8 GB DDR3 (2 DIMM)". That means you would have to buy two 4GB modules to upgrade to the full 8GB ram. Find others and do the same research to see what ran thy will support. Good luck.