Inspiring 6400 upgrade to 4gb

[qwertyjjj]

Got an old 6400 with Max 2gb ram. Some say the bios can actually take 4gb bit I need to downgrade from A17 to A09 version. Any thoughts on if this is ok?
Is it also easy to upgrade the CPU in these?

 

[qwertyjjj]

Win 7 64 installed.
Windows says I have v4gb installed but only 3.24gb ram is usable. Any ideas?
T7200 4gb 64bit OS
I see the same message in the bios