Hello teachme,
The RAM on the Galileo is 256MB and cannot be expanded unless you make major changes to the Galileo hardware, if this is the case and you want to replace the RAM chip, you should refer to the Quark SoC X1000 Datasheet. Check the section 13.2.1 System Memory Technology Supported.
However I must warn you, if you decide to proceed to make this changes, you will not be able to apply for a board replacement in case your board gets damaged.
Peter.