Should I uninstall TT2017 before I install TT2018?

[xmasbaby0]

Not necessary at all unless you really need the space on your hard drive.  You need the program in case you want to open up a 2017 file.

[taxdudethree]

More importantly, if you keep the prior year program and files, you can save time and effort by importing your basic personal data from, e.g.,  your TT2017 file on your computer into the new TT2018 file.  You don't have to, but it helps a lot if you stick with TurboTax year after year.  And there's no issue of security compromise, as the data is going from one spot on your computer to another.

[taxdudethree]

BUT I don't know whether the new TT program needs the prior program to be on the computer, or merely the prior tax file.  I always leave both of mine (programs and files) on the computer.  One more tip:  when you file your return, make sure you keep both the file as well as the .pdf file TT allow you to make, and for both go to "Properties" (on a Windows machine) and change the file attributes to "read only" so that when you may open the file in the future and perhaps change a number or whatever, it can't change the file you're using as an archived file for what you actually filed with the gov't.  If marked 'read only' and you do click 'save file' it won't change the 'read only' file but will offer to save the file with a new name.  

[Bsch4477 · Accepted solution]

If you remove the 2017 program the tax file remains on your computer so information from 2017 will still be carried over to 2018.  But as xmasbaby0 mentioned, you will not be able to see your 2017 return in Turbotax if you remove the program.  Of course you can still see it if you made a .pdf copy of it.