How to open Asus ET2400 series



is it possible to change the motherboard so I can change the graphics card ?
 


Almost certainly not. An AllInOne is more or less a laptop, in a different configuration.
All of the parts are designed around each other. MB, case, ports openings, cooling....all designed as one piece.
The only possible way would be if there were a better motherboard, from that exact same series, that actually fits that case perfectly.
They are not meant or designed to be upgraded.

All In One - all the limitations of a desktop (non-portable) with all the limitations of a laptop (non-upgradable). And none of the advantages of either.
 


if it possible, how do I know if the motherboard is compatible with processor and graphics card ?