If you want to utilize the capabilities or the features of Windows Phone 8 in your Windows Phone 7.5 project, you might need to upgrade it to Windows Phone 8.
Once you upgrade your Windows Phone 7.5 project to Windows Phone 8, you cannot revert back and hence it always better to copy/backup your Windows Phone 7.5 project before upgrading.
Upgrading Windows Phone 7.5 App to Windows Phone 8 in Visual Studio 2012.
To upgrade the project to Windows Phone 8, follow the below steps
1. Open the Project. Right Click on the project and click properties.
2. In the Properties Dialog screen, you will find the “Target Windows Phone OS Version” dropdown which lists
- Windows Phone OS 7.1
- Windows Phone OS 8.0.
3. Select “Windows Phone OS 8.0”. This will display a confirmation dialog. Click “Yes”.
4. Immediately, you should see your windows phone project being upgraded to Windows Phone 8.