I'll give details regarding the upgrade process and what to do with older QuickBooks Desktop versions.
I take it that you're using a multi-user setup. You would need to upgrade QuickBooks Enterprise to the same version (2018 or later) for your other PCs. You would just need to upgrade the one you're using, not necessarily all of the editions (Pro, Premier, etc).
Also, you have the option to keep the 2017 version so there's no need to revert the new version. During the installation, there will be a prompt if you'd like to keep or remove it from your PC.
Take note that when you convert and open the company file on the 2018 version (or newer), we're unable to use it on older QuickBooks Desktop copies (version 17 in your case).
You can check the company file upgrade guide if you need help: Upgrade your company files after switching to a new version of QuickBooks Desktop.
After installing, I'd recommend reading our articles if you need help getting things done in QuickBooks Desktop. You can also open the built-in Help feature. Simply press the F1 key to open the Have a question? window.
We're open around the clock, so don't hesitate to post again if you have more questions for QuickBooks Desktop. If you have follow-up concerns regarding the installation, just include them in your reply below.