The easy way would be:
- Open explorer and go to "This PC"
- Right click on the drive you want to encrypt
- Choose "Manage Bitlocker encryption"
Here's also a tutorial about how you can enable the usage of AES-256 bit encryption instead of AES-128 (which is default). The first one is slightly slower but much safer according to NSA. Enable AES 256 bit encryption.
The tricky part here is however what unlock method you choose, entering the passphrase on boot may be tricky. While it shouldn't be any trouble considering that you have access to the KVM terminal which is like connecting your machine directly to a monitor I'm not fully sure that works. The physical hardware should be modern enough to have TMP modules but I hardly doubt those are accessible by the virtual machines (Linux host and Windows guests).
You may get away if you load your keys from an external server (hard to setup and requires network access) or if you use a small local FAT32 partition to store the keys. In any case I think Bitlocker in this environment would cause more trouble than what it solves. I'm pretty sure that KVM does some encryption on the virtual drives so disk encryption won't really be needed unless you have a multi user system of course and want to prevent users from accessing other users files.