Welcome to the discussions!
There are two passwords on the Time Capsule
1) Device password to access the setup and disk
2) Wireless network password
If you setup the Time Capsule on a Mac, you should be able to retrieve both passwords from KeyChain Access.
Your post indicated that you are using a PC. If that is the case, your only option is to return the Time Capsule to factory defaults and reconfigure the device with new passwords. This will not affect the the stored data on the disk.
Please post back to clarify on whether you setup the TC on a Mac and need assistance with password retrieval, or whether you need instructions on how to return the TC to factory defaults.