How do i safely format my phone?

I have a Nokia Express Music 5570 (i think, something like that anyway) and i'm not sure whats wrong with it but the C drive, phone memory, seem to keep losing memory whenever i use applications recently and i have to keep deleting things to keep it from 0kb and be able to use messaging and other applications.

If you have an idea what may be causing this please tell me because is has never happened before.

Otherwise, do you know how i can restart my phone? I think i need to backup the data and restart my phone. do i just remove the sim card and put it back in again?

Thanks for any help :)How do i safely format my phone?
Save all of your pictures and whatnot on a memory card, pull the memory card out, and do a factory reset on your phone. Google your phone's model and make, it will give express intstructions on what to do.How do i safely format my phone?
Backup everything to memory card and all contacts to your SIM or memory card or PC. After you've done that, type in *#7370# and you'll be prompted for the phone format. Complete that, you'll free your phone memory. Now, after you've done that, go to Menu %26gt; Applications %26gt; LifeBlog %26gt; Settings %26gt; Item Types %26gt; Uncheck everything. You will not have any further problems with phone memory unless and until you fill it up with junk.