How do I renew the Solidworks Student License?

Hello community, 

So there you go, I downloaded Solidworks last year for the 2018-2019 school year and today I have to renew the license so I uninstalled it but when I reinstall it it tells me that the license has expired. The problem is that there are solidworks files that I can't delete (it puts me that the file(s) are open in another program or I closed everything) so I want to know if it's because of that and especially how can I delete them permanently.

Thank you