Quick walkthrough of the process of iunstalling the Windows Phone apps by downloading them to the PC and then sideloading the XAP or APPX Files on the Windows Phone.
Windows Phone 8.1 has hugely improved this feature and copied installation files appear up almost instantly in the Store, unlike the way it happened earlier with Windows Phone 8.0 and required resatrt.

Read more here – http://www.techmesto.com/installing-downloaded-apps-wp8-1/