Since you are enrolled you are a student, no more a guest. In order to change your guest account into a definitive Unitn student account please login one more time with your guest account to MyUnitn. The system will automatically ask you twice a new password and inform you about your new username. 

Please note that you student username can be really different from your guest account!

For instance:

miss Hermione Jane Granger

could have got a guest account h.granger.1

and receive a student accountt hermionejane.granger

Look out carefully!

If you don't remember your provisional guest password you can retrieve it (https://www5.unitn.it/Registration/en/Web/RememberPassword) or contact helpdesk (https://webapps.unitn.it/servicedesk/support/en/public/SRV0000266).