You can locally and remotely control the volume of your music from a web browser when playing from any device. 

If you are playing music in a browser (in Tune), you can control the music's volume currently streaming using the player bar at the bottom of the screen.

If you are on the Manage or Message Plan, you can also control the volume of your remote locations that are streaming on any device (Browser, Mobile or CloudBox).  

Log into Tune as the Admin account, and select 'Account' at the top of the screen.

From the Admin navigation on the left, select 'Zones'.  You should now see a list of all your locations.  Find the streaming location using a web browser, and click on the volume button.  A slider will display for you to change and set the volume.

Additionally, you can change the player bar into a remote, and change the volume that way as well.  Toggle the switch from 'stream' to 'remove' and select the zone you wish to change the volume for.