Welcome to Nokia forum! 
The phone notifies you if the phone memory is getting low. To free phone memory you have the following options:
- Move data that you want to keep to an alternative memory (mass memory or memory card, if available) or to a compatible computer.
- Remove data you no longer need.
Use File Manager or the respective application in your phone to remove data or to move data to alternative memory as described in the user guide. Typically you first mark files to be removed or moved and then you select the corresponding option (Delete or Move to folder).
Use Nokia Suite to move data to a compatible computer.
To maximize free spaces to your phone memory, you can remove or move the following:
- Messages from Inbox, Drafts and Sent folders in Messaging
- Retrieved e-mail messages from the phone memory
- Saved Web pages. Clear the web browser cache to free some phone memory (e.g. select Options > Clear privacy data > Cache).
- Saved images, videos, or sound files (in Gallery, Photos, Videos or Music player)
- Contact information (in Contacts)
- Calendar notes (in Calendar)
- Downloaded application packages
- If there are applications which are not needed any more, uninstall them with Application Manager
- Any other data that you no longer need
If you are deleting multiple items and any of the following notes are shown: Not enough memory to perform operation. Delete some data first or Memory low. Delete some data, try deleting items one by one (starting from the smallest item). After deleting data, restart (power off/on) your phone.
Hope this will help you my friend. 
