Upgrading Ram need help deciding how much I need

[slashobeint]

I have the Acer Aspire TimelineU M5-481TG-6814 Ultrabook which comes with 1 slot of ram and 1 unchangeable 2 gb of ram. Through the comments it says it can handle 10 gb of ram instead of the 6 gb restriction said by newegg. Should I just buy a 4 gb ram stick or go with 8? And what would be a good buy for ram?

The laptop:
http://www.newegg.com/Product/Product.aspx?Item=N82E16834215392

 

[DarkSable]

Are you sure the second stick is unchangeable?

I don't have much experience with laptops, but usually ram has to be of the same brand and amount, or else you get problems. But that would cap the laptop at 4GB of ram...