Which version of Hoster are you using ?
Various ways to do this, one easy way is to open C:\MTU folder and rename the Hoster Folder to something like HosterBackup and the KMA files folder to KMAbackup disconnect any external drives if you have them connected. Then start Hoster and it will build a new Hoster folder with an empty database for songs and singers. If any thing goes wrong you can delete the new Hoster folder rename the 2 folders back to how they were and restart Hoster as normal.
When you are satisfied you don't need the backup folders you can just delete them.
Option 2
This appears slightly different according to your version but from the build database dialog, remove all folders from the list of folders shown, then when that list is empty and not showing any files press the rebuild database option.
This will build you an empty songs database and be like starting from new except it still leaves the singers database but this can be deleted after-wards from within Hoster.
When you say delete and start over, if you original music was imported from CD+G disc's as KMA files and you were to delete all these files you would have to re import all those disc's over again, quite a time consuming thing if you have a lot of disc's
If you Add that KMA folder back to the list of folders then nothing will have changed, it will rebuild them back as they were as all the information Book id, Disc Id is built into the KMA headers.
If you imported them as mp3+g or zip as KMA files and did not keep the original mp3+g or zip file then these files would be lost.
One way out of this dilemma is to convert all you KMA files to mp3+g or zip files instead of deleting them. This will allow you to re import them from scratch as Hard drive imported files without all the original Book id data that can't be changed in the KMA file.
To do this you would need Songverter that is available from the main MTU site.
If you imported your files via mp3+g or zip as KMH files you could just delete the KMH headers in the folders then you would still have your original files to start over with. To just delete the KMH header files open the folder containing them and right click on a blank area in the folder and from the options fly out select "Sort by then if it's available select "Type", that will list the KMH headers separate from the other files so you can just delete those.