My lumia memory is low.

If your phone's memory is low, then remove things you no longer need. In many cases, you may not need to keep some files on your phone.

• For pictures and videos you can use Microsoft SkyDrive as additional storage. To increase free space on your phone, move pictures and  videos from the camera roll to the SkyDrive.
• Remove old Office files on your phone (press Start, then swipe left to App list and click 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).

In Windows Phone 8, use the Storage Check application. With this app you can view the whole information of the phone storage, remove downloaded maps from your phone and clear temporary files, such as leftovers from app installs and updates, Sky Drive uploads and PC file transfers. Go to Settings > Storage check, swipe over to the Details view. 

To get Storage Check app, you need an updated version of Extra info system app. Once Extras info sys app updating is complete, Storage Check appears in the settings menu.