how do i update my old version of toast. I paid for an upgrade to titanium 20. what now?

If you made this upgrade purchase online at Roxio, then I suggest the best avenue for support will be through them.

I expect you should be looking for an emailed receipt from them with instructions for download and registration.

Roxio: https://www.roxio.com/en/products/toast/

Issues like yours need to be addressed directly with the vendor.