Wyse R90LEW and WES 2009

Wyse R90LEW and WES 2009

I have a few R90LEW's with WES 09 on them and I would like to upgrade the memory. They currently have 1 GB installed. I know that the this model comes with up to 2 GB. Does anyone know if this is the limit of the OS/or hardware? Can i put up to 4 gb in there? These machines are less than 1 year old.

Thanks in advance.