Currently, there is no way to take an existing top-level category and make it a sub-category. For example, I have two top-level categories, Network, and VPN. Let's say I want to move VPN to be a sub-category of Network. There is currently no way to do this. You must delete the VPN category and then recreate it as a new sub-category. Solarwinds Web Help Desk easily handles this process.