Should I uninstall Endnote 2021 first or is it suficient to install over the existing Endnote 2021?
If I uninstall the previous version will it retain my preferences and the styles I modified and saved as my custom styles?
This sort of question is best addressed to EndNote technical support, EndNote. They’ve been pretty prompt and helpful in my last few interactions. However, I’d suggest removing EndNote 2021 first. I don’t think you HAVE to because on Windows it installs an “EndNote 2025” folder so it shoudn’t overwrite. However, the CWYW EndNote add-in to Word has to point to one or the other, and I could see it getting confused. Likewise, you might get confused having same named Style filters in different places for different versions. In my last reinstall of EN 2025 for a new computer, I had to install the Word add-in manually, but that might have been some corporate security messing it up. So I can’t see any advantage to keeping the older version on the same computer as the newest.
Regarding preferences and custom styles, I’s suggest manually find and make a copy of the folder containing your custom styles. You shouldn’t lose them, but if you modified styles without renaming them I could see them getting overwritten. Better safe than sorry. Some preferences seem embedded in the *.enl file, but I usually lose most of my preferences during upgrades or moves. This includes resetting file locations to wherever you saved those custom styles. My low-skill solution for saving preferences has been to take screenshots of the different preferences windows so I can remember what they were when resetting them. Tedious. Maybe someone else will reply with a smarter way.
I do not use CWYW as it has always been fragile. I export references to BibTeX and use LaTeX. I kept my 2021 version (that I prefer) when I installed EN 2025 (that I now regret purchasing) on macOS. I have never had any issues related to having more than one EN version installed.