I want to remove Webroot that Best Buy installed on purchase. When using Finder to put Webroot in Trash, this appears: "This operation can't be completed because you don't have permission to access some of the items." How to fix?

It looks like the uninstall is a simple process:

https://answers.webroot.com/Webroot/ukp.aspx?pid=17&ruleid=2130

You will probably be asked to enter the password you used to log in to you Mac. That's normal.

You let someone at Best Buy touch your Mac? What else did they do to it?

Did they create an admin account that they used to destroy your Mac from?

If so, can you log into that account and move the app to the trash?

If not,

Select Webroot in the Applications folder and Get Info (cmd-i).

Click the padlock at the bottom of the list under Sharing & Permissions. Authenticate with an admin account.

Add your user to the list by clicking the + button.

Select your user and see if you can set your user as the owner from the gear menu below the list.

You should be able to move it to the Trash, then restart.

Since there is no way to tell what the idiots did to your Mac, you may just want to erase it completely, reinstall the OS, then migrate your user information from a Time Machine backup. You'll need to create a Time Machine backup on an external drive first.