In the Extensions and Updates window, select Available Downloads and enter QTouch in the Search box.
Select QTouch Library and click Download.
Sign in to Gallery Dashboard
The next window will ask you to log into your myAtmel account.
If you don't have an account you can create it at this point by clicking on the link by New User?.
The QTouch Library will start downloading and you will be asked to agree to the License Terms before Installation can begin. Click on Install to agree to the terms.
Click image to enlarge.
The QTouch Library will finish installing and you will be asked to restart Atmel Studio for the changes to take effect. Click on the Restart Now button in the bottom right of the Extensions and Updates window.