Uninstall or delete modules when upgrading 6 to 7?

Question

Sorry to ask such a basic question, but I can't find an answer (and I'm an amateur).

I have a website that was written for me in Drupal 6. I want to upgrade it to Drupal 7.

There are quite a few contributed modules, and I realise I need to disable these before upgrading the core. Can I then simply delete the unused modules via FTP, or do I have to use uninstall within Drupal?