Remove or move things you no longer need on your Lumia Windows Phone 8, use the Storage Check application. Go to Settings > Storage check, swipe over to the Details view:
- Remove downloaded maps from your phone and clear temporary files.
- Tap on apps details to find out what apps you have on your phone, consider uninstalling some of them to increase the space in your phone memory.
- If you have a PC, connect your phone to a computer with a compatible USB cable. On your computer, use the Windows Explorer and browse to your phone to see a list of the folders: Documents, Music, Pictures, Ringtones, and Videos. Right-click the file you want to move, click Cut, right-click a location on your PC, and then click Paste.
Remove old Office documents on your phone (press Start, then swipe left to App list and tap Office).
Delete browsing history, temporary files, cookies and saved passwords in Internet Explorer (Settings > applications > Internet Explorer > delete history).
Delete previous map searches and temporary files from your phone (Settings > applications > maps > delete history).
Delete Bing search history, including Bing Vision and Bing Music searches (Settings > applications > search > delete history).