In order to hard reset a Sony Ericsson K510, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Sony Ericsson K510 device will be brought back to the default configuration of a brand new device.
1. Switch on the phone.
2. Now select Menu > Settings > General > Master Reset.
3. Voila, the phone should now reset and restart.