If for some reason or another you want to delete a track from the workshop (because you uploaded it on accident, for testing, etc.), simply deleting it from the workshop may not be enough.

If you wish to completely delete the track from your client as well, you must delete the files manually.

On Windows, the files should be located in:

C:\Users\<Your Username>\Documents\My Games\Distance\Levels\

At this point you should see two folders. "MyLevels" and "WorkshopLevels".

Levels that you've worked on using the level editor are contained in MyLevels.
As far as I know, when you "delete" a level you've worked on, it converts the file into a .png.
No idea if this is actually the case, somebody please clarify this if you know for sure.

The levels you've downloaded from the Workshop (including your own) are contained in the "WorkshopLevels" folder and sorted by creator. Each creator has a number assigned to them (e.g. mine is 76561198025919450. Hopefully this isn't sensitive data of some sort... :P). To delete those maps that somehow remain on your track list, these folders are where you can find them.

When trying to reset leaderboards, a problem people may have is that they've deleted the file off of the workshop and their local files, reuploaded it, and still see their personal leaderboard as it was before.

This is because leaderboards (your own) are stored elsewhere, and it reuploads your personal copy of the leaderboards to the global leaderboards when it has the chance.

To prevent this, navigate to:

C:\Users\<Your Username>\Documents\My Games\Distance\Local Leaderboards.

Here you should see three folders: "MyLevels", "OfficialLevels", and "WorkshopLevels".

If you're trying to reset the times for a track you've made, go to MyLevels.
Official and workshop times are self-explanatory at this point. Go to their respective folders.
Once again, workshop level times are sorted by a unique creator ID, so you'll have to do a little digging if you're played many tracks.

I hope this has helped!