To add or remove backgrounds from the Windows version of Teams:
- Right click on the Windows Start menu
- Select File Explorer
- Add the following to File Explorer's location bar:
%LOCALAPPDATA%\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams\Backgrounds\Uploads
- Add or remove backgrounds in the displayed folder
The changes will be visible when you next use Teams. The preview pane may show images in reverse, but display correctly in your meeting.