If I were to write it in a flow chart, here's what I'd say :
STEP 1
Check if Under warranty, if the warranty is claimable in your country(locality).
STEP 2a
If YES go to service center and do not do anything that voids your warranty.
STEP 2b
If NO, then boot into your BIOS and find out the motherboard model. OR Open up the laptop and check the model number or part number printed on it.
STEP 3
Google the ****** out of that model/part number. You will easily find out how much ram it supports.
STEP 4
Make sure you use a 64bit windows as 32bit windows only supports upto 4gb
STEP 5
Chill
STEP 6
Eat bacon.