First decide how the present equipment is or is not doing the tasks you want it to do, and if it is satisfactory.
Then decide on a budget and if that will be enough to do a proper upgrade to the level you need.
Then go over the choices of parts to see:
-compatibility with parts you might not change;
-software compatibility with new parts and old parts working together;
-prices and availability of parts you need;
-possibility of recycling old parts to do good or selling;
-if you are up to the skills needed to do that upgrade.
I tried to upgrade an older video system with a new GTX 750 ti years ago. Only after getting no activity from it, I learned it was not compatible with my motherboard BIOS, and no solution. This was not on outside of box, or instructions, or known by customer support. I had to swap it into a less desirable computer system, since I could not get a refund.