Install

1. Save your project.
2. Go to the top menu bar and click Edit (or Blender on macOS). Select Preferences.
3. In the Preferences window, click on the Add-ons tab.
4. On the top right click on the drop down arrow and select Install from Disk…

1. There select the .zip file of the Add-on you downloaded and click Install from Disk

Remove

1. Save your project.
2. Go to the top menu bar and click Edit (or Blender on macOS). Select Preferences.
3. In the Preferences window, click on the Add-ons tab.
4. In the search bar on top, type the name of the add-on to remove.
5. Click on the drop down arrow on the left of the name of the add-on to extend it.
6. Click on the check box of the add-on to disable it.
7. Click on the Uninstall button.
8. Close Blender and re-open it.

Update

1. Save your project.
2. Remove the add-on.
3. Close Blender and re-open it.
4. Install the new add-on.