That looks to be an OEM motherboard, old one at that. The case it's in may not support a replacement motherboard, and since the thing is so old you need to get new RAM for it. You are better off selling or scrapping the system and getting a new one, or at least a newer used one. Upgrading to an Intel i3 system, or anything similar, would take to many new parts you may as well just replace the whole system.
A used computer with an i3 should be maybe $150 for a basic non-gaming setup, which is how much a new CPU and motherboard would cost even at a very cheap motherboard.