No you can't use 2018 to amend another year. You need to use the same year program. You don't need to keep the programs installed but you will need to reinstall them if you need to amend or open the .tax file for that year.
When you are finished filing you should save your return as both the .tax file and pdf file. Then you won't need the program installed if you need to print a copy in the future like to get a loan.
