Hi,
I have a trial version of Nuendo currently running on my computer. I took advantage of the Mega Sale and bought a regular license. Now I see them bodth listed on my Products page list like this:
The trial version is exactly the same as the regular installer, so you don’t have to do anything. But if you want, you can deactivate the trial license in the Steinberg Activation Manager and activate the regular license in its place.