Ah, right. If you want more memory, speak to whoever you purchased the machine from and ask about the warranty.
It may or may not invalidate the warranty, I really don't know but my money would be on yes, it makes the warranty null & void.
If you can fit it yourself, with a laptop it normally involves undoing 1 or 2 screws, lifting a cover, and inserting new modules into slots, possibly having to remove the old modules first.