Need help upgrading PC?

So I have this PC (HP Compaq 2600 Pro), it comes with a 2nd Gen I5 3.1 Ghz 4 Cores 4 Threads, Hewlette Packard 1497 motherboard, (I upgraded to 16 GB DDR3L RAM so I m not interested in upgrading that). I want to upgrade my motherboard and PC but keep my RAM the same. What would be the best? Thanks!
Update: Update: Just letting everyone know I already have an SSD and a GTX 1050Ti, and when opening task manager the only thing at 100% is my RAM (which I am replacing soon) and my CPU.
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