In order to change the download and installation locations for your games in the Uplay client, first click on the 3 horizontal bars located next to your news/game/shop buttons.
Once you’re on the Settings screen, You’ll want to navigate to the Downloads menu on the following screen.
This will show the current location of your download and installation directories, which can be changed, or set back to default using the buttons located under the file paths.
For further assistance with the Uplay client, we recommend contacting Ubisoft support HERE.