Assuming you don't back up other computers to the Time Capsule, the most straightforward thing to do is open up AirPort Utility, double click on the Time Capsule on the left, and then go to the Disks tab. Under that you can select the Time Capsule drive and do a quick format or a secure format. If you just want to delete the sparse bundle created for your computer, you should see the Time Capsule in the Finder sidebar under Shared, and you would find the sparse bundle with your computer's MAC address or computer name and delete it manually by putting it in the trash and emptying.