you should be able to find the max ram limit on gateway's website. it's likely 2 or 4gb, but i wouldn't be surprised if it's limited to 1gb.
also keep in mind that windows 7 starter is limited to 2gb. even if the netbook can physically accept 4gb it won't be much good unless you upgrade windows too.
with that said, i was in the same position with my netbook last year: it came with 1gb and windows starter and was sluggish. i upgraded to windows premium and threw 4gb in, but what really made the biggest difference was upgrading to a SSD. you might want to consider that also/instead.