Hello!, the truth is that I had a 901 and I still have a 1000H, but I barely remember the first one and the second one changes quite a few things.

From what I have seen in several places, this Eeepc only has one RAM slot and it seems that it can hold up to 2Gb DDR2 667, so you would have to change the 1Gb for one of these. 4Gb is not supported even by the 1000H which was a bit more advanced.

I would look for a module on Wallapop or similar, if you don't have someone handy who might have one to spare, since it can cost you nothing and less.

Best regards!