I'm confused about something regarding this awesome game. After completing the first stage, I was able to view the upgrade screen where I can unlock special abilities. I was unable to upgrade any of my abilities at the time, so I started the second stage. I immediately ended the game because I wanted to start the first stage over because I didn't get all three medals based on my score.
I completed the first level with the three medals, however it didn't give me the upgrade screen. I moved onto the second stage, completed it, and moved onto the third stage without getting the upgrade screen yet again.
So now I don't know how or where to upgrade my character and can't find anything addressing this online, so am I missing something obvious or is this a bug?