You can delete a Category in Project Settings. You won't lose the Cards, but will be asked to nominate another Category to move them to.
1. Go to Project Settings and select the Card Category tab.
2. Click the three dots next to the Category you want to delete. Click "Delete".
The Delete Card Category window will open.
3. Select the Category you want the Cards moved to.
Note, you will see an alert about which fields are not on the destination Category, and therefore you will the lose data. If you don't want to lose this data, you can add the fields to the destination Category before deleting the Category. See "Edit a Card Category" above for details.
4. Click "Delete" to delete the Category.
Please let us know below if you found this guide helpful.