then set root passwd to whatever you want.

https://www.itzgeek.com/how-tos/linux/linux-mint-how-tos/recover-your-system-with-single-user-mode-in-linux-mint-linux-mint-12.html

You can skirt around the user but not admin. Some newer versions deviate from this. I'm assuming you didn't encrpt your drive.

If reinstall is easier for you go ahead but that's just an M$ habit. I have rarely needed to reset but there are a couple ways to get by the passwords. One is adding a command to the end of your install line in your GRUB edit menu, the other is drop to single user from rescue mode or from a command line in your splash screen if it's there. Sometimes you can to drop to single user by holding key combinations at startup and enter a command. I'd give you exact instructions but I'm not privey to my servers at the moment and it's been years since I've needed to do it, sorry. Plenty of info out there. Good luck.

so a reinstall is no big deal. When I installed it from a thumb drive, it asked me if I wanted to format the hard drive, so I'm guessing there shouldn't be remnants of this installation if I do that again.

This time I'll watch out for passwords!

anyway you want or just do the auto setup which sets partitions (root and swap) and formats automatically.
If there's one thing I do manually it's chose my own partitions. I like to make a separate root, home, var (variables) swap and another that I use for storing stuff. If one part of the system gets borked, usually root or var, I can reinstall the root and var and not format my saved stuff or home. If they're all one partition you can lose all of it. Var is a file where all variable short term files are written and rewritten by programs. Many times when something goes wrong it's the temp files used by programs in var. I keep it separate so I can fix problems without messing with anything else. You're ok hitting auto though. I just like making things complicated.

When I start using it for serious work, I'll get into some of this stuff.

While I'm at it, thought, is there anything that can read WordPerfect files. And has the "show codes" trick that can be invaluable. LibreOffice drives me crazy with formatting at times.