Removing old files

I have clone a drive to an SSD Drive, how can I remove the Windows files from the old drive without formatting it.

If you don't want to format the old drive (why not?) then you can just delete files as normal. You may want to enable seeing system and hidden files to make sure you can get everything. Hidden Files, Folders, and Drives - Show in Windows 10 - Windows 10 Forums

However you are almost certain to run into permissions issues so unless you want to spend ages trying to figure out how to delete old files (you'll need to take ownership and grant authority as described in the tutorial below) you would almost certainly find it easier to format the drive.

Owner of Files and Folders - Change in Windows 10 - Windows 10 Forums

It is certainly possible to delete things manually but it will take you a lot longer than just formatting the drive if there is nothing you want on it.

You may also (depending what your plans for the old drive are) want to consider writing zeros over the deleted files as this would prevent someone recovering your deleted data if you plan on selling/chucking the old drive. CCleaner can do this.