Open PowerShell with 'Run as administrator'. Then type the following commands.

manage-bde -status

BitLocker Drive Encryption: Configuration Tool version 10.0.16299
Copyright (C) 2013 Microsoft Corporation. All rights reserved.

Disk volumes that can be protected with
BitLocker Drive Encryption:
Volume C: []
[OS Volume]

    Size:                 476.34 GB
    BitLocker Version:    2.0
    Conversion Status:    Used Space Only Encrypted
    Percentage Encrypted: 100.0%
    Encryption Method:    XTS-AES 128
    Protection Status:    Protection Off
    Lock Status:          Unlocked
    Identification Field: Unknown
    Key Protectors:       None Found

Disable-BitLocker -MountPoint "C:"

   ComputerName: MyComputer

VolumeType      Mount CapacityGB VolumeStatus           Encryption KeyProtector              AutoUnlock Protection
                Point                                   Percentage                           Enabled    Status
----------      ----- ---------- ------------           ---------- ------------              ---------- ----------
OperatingSystem C:        476.34 DecryptionInProgress   8          {}                                   Off