Can I change my user profile?

Yes. In order to change your user profile you only have to apply for it. Having into account your billing cycle, you will pay the proportional part for the days left until the next invoice. 

For example: 

-   Your billing cycle ends the last day of the month and you have a commercial license of 15 € / month.

-   You change to a manager license of 19 € / month on the 15th.

-   In the following invoice you would pay half of the commercial license and half of a manager one; that is to say, 7,5 € + 9,5 € = 17 €.