Use the File Manager
Click the "Menu" button at the bottom of the home screen. Navigate to the "Organizer" icon in the final row of the grid and press to open.
Select "My Stuff" from the top of the list. This will open the Sony Ericsson file manager. Some Sony Ericsson phones will have an icon for the file manager in the main menu.
Click "Options" in the bottom left-hand corner of the screen and choose "Memory Status" from the list of options. A dialog box will appear that shows you the amount of available space on your phone and, if applicable, on your memory card.
Press the "Phone" button and select a folder from the list. Highlight a file using the navigational keys and press Delete" to erase.
Perform a Master Reset
Click "Settings" in the main menu.
Scroll to the bottom of the "General" tab and select "Master Reset."
Click "Reset all" to completely erase the phone memory and return the phone to its default factory settings. Press "Continue" when prompted to confirm.
Tips & Warnings
Always make sure you have a copy of any files you wish to keep on your personal computer.
Performing a master reset will change all personal settings to the default Sony Ericsson settings
Use the below link for unlocking the phone
http://www.theunlockspot.com/sony-ericsson-w518a/rs10wp9/http://www.unlocking4u.com/sony-ericsson-w518a/rs6wp9/Good luck..