Thank you for your quick answers and additional questions.

I didn't buy the usb drive but the download 2018 upgrade. The 2016 program I have on BIAB disk. I installed that one on my laptop, but it takes a lot of space, and will even be more after 2018 upgrade. So that is why I want to transfer the whole program to an external drive when I upgrade. I only have one 2016 license left, so I want to keep that in case...

I am not sure what the upgrade does. Will it overwrite the 2016 program? If that is the case then it likely will not be a problem to assign a different location. But if it only adds new facilities to the existing one then it will be different, I guess.

I also don't know how much space the upgrade will need. I have read somewhere that the downloadable version will need 100 Gb plus 100 Gb for the instellment.