Open CONTROL PANEL
Set VIEW to SMALL ICONS
Click on "BitLocker Drive Encryption" towards the top of the window.
Each drive should be listed, stating whether BitLocker is ON or OFF. Then, simply select whichever drive you which to En/Dis/Able BitLocker on.
WARNING: If you turn BitLocker ON, it should prompt you for a password, and the option to print a recovery key, and/or generate a recovery flash-drive.
BE SURE to have as MANY recovery options as possible!
If something goes wrong and you don't have any of these, you can consider your data LOST FOREVER.