You can upgrade by opening rooms in your dorm and putting people in them, then leveling those people up.
To those asking to be vollied: I'm assuming you want to be vollyed (hired back and forth) to earn money and upgrade. Being volleyed is not the most effective way of making money. I would recommend partying or farming for money. Here is a list of farms, before hitting make sure they are inactive because occasionally some people become active again and may hit back. To party, join a club, and hit the party. If you can, I would recommend joining Cat Cafe or Pizza Pop (Art) because they pay the most. You will get money once the party is successfully completed. Here is a link to a thread naming some clubs that have no stat limit. You will earn 2x as much money per hit if you have 15m x your kcs in tutors. Once you earn the money, and probably before too, check out some of the threads in the strategy and guides section of forums This guide explains how to get started I'd check it out first. Also, if you need help or more suggestions feel free to ask me.