I already filed my 2020 taxes and received an amended W2, do I EDIT the current one or ADD NEW?

You edit the one you already have in the system ... that is what a corrected W-2 form does ... it replaces the earlier one that was issued ... it is NOT another W-2 form. 

You didn't say, but I hope you are filing an amended tax return, Form 1040-X. Just editing the W-2 in TurboTax, after you have already filed your tax return, doesn't do anything.

Go to the following link for instructions to amend a 2020 tax return that you filed with TurboTax.

How do I amend my 2020 return?

It normally takes the IRS 16 weeks to process an amended return. But they are severely backlogged this year, so expect it to take much longer than that.

Don't file the amended return until your first return has been accepted and you have received the original refund.

what boxes got changed? some changes are informational only and therefore filing an amended return is not required.