Do you Google? Motherboard Specifications, M2N68-LA (Narra6) - HP Customer Care (United States - English)
One word of warning: there may be multiple revisions of the board out there. This might
match yours. The "Narra6" part may uniquely idnetify the model, but I'm not certain.
Phenom2 x2 555: it's on the supported CPU list.
10GB RAM: no. 2X2GB is the max. The board has only two RAM slots.
BIOS version 5.20: No idea. Asus made the board, but they usually don't directly provide updates for OEM boards like this one. If the board is still in the original HP (Compaq) case, check downloads for the exact model. The downloads may include a BIOS update. If you're searching the Web for an update, be cautious. There are sites out there that are trying to give you other things than a BIOS download.