How do i reset my blackberry 7250?

A "soft reset" can be performed with "shift-alt-del".

A "hard reset" can be performed with the pin-button under the battery cover or by removing the battery.

If you are trying to do a factory wipe or reset then you should enter the wrong passWord 10 times for an automatic wipe and then follow the security policy removal steps.

If you are trying to remove the cell phone company's "sim lock" on your phone you will need to contact your provider or buy an unlock code from someone on ebay.