Its very simple.
1)First backup all your data to your computer using NOKIA PC SUIT.
2)Just remove the SIM CARD and the MEMORY CARD.
3)Go to menu-tools--settings---general---factory setting.
4)You are done. Your phone will re start with original factory settings..
5)Use NOKIA PC SUIT to restore all data again to your NOKIA E63.

http://ezmeans.com/2012/11/10/nokia-e63-memory-full-4-effective-solutions/

Nokia E63 Memory Full – 4 Effective Solutions

If you’ve been using Nokia E63 for more than a year, you are likely to get repeated annoying notification that “the memory is full. Delete some data to send and receive messages”. Though you delete all messages, the problem does not seem to get resolved. This is very annoying because you can not do some basic operations like receiving and sending messages, with this problem on.  Here are a few things that you can do to get rid of this problem once and for all. 

1. Backup phone memory to memory card -
This is my number 1 method of solving this issue. Go to Menu – Tools – Memory. Click on options and click on “Back up phone memory”. This will backup everything onto your memory card. This has been solving my issues for many a times.  

2. Clear Cache of the internet –Click on the internet button that you can see on the default screen. (Let it load the internet page)
Click on options, scroll down , click on “clear privacy data” select all. Click Yes. This will clear all privacy data and unload the phone and give a lot of memory.

3. Remove unwanted Apps –Chances are that you are have downloaded a few apps that are not useful to you anymore. Go to app manager and delete them.

4. Store most of the things in memory card – Store all your videos, audio files, active notes etc in Memory card rather than on your phone.
To store all active notes in memory card – Click on active notes – options – settings. First in the menu is memory in use. If it is showing ‘phone memory’ then change it to ‘memory card’.