Want to upgrade to Mac OS High Sierra and it shows MediaKit reports not enough space on device for requested operation
Typically this means you need to erase your drive. It could be a permanent storage error, but most of the time you can fix things by erasing the entire drive and reinstalling.

MediaKit reports not enough space on device for requested operation
Unable to format Mac internal drive (disk0)

Do you need time to back up or instructions to erase and install macOS?