2 Jan 13, 2015 05:42
Regarding your questions:
1) Yes, you can do it. It is safe.
2) It depends on which upgrade method have you been using until now. If you followed this one: http://b2evolution.net/man/upgrade-instructions, the 3rd step ensures that you will get rid of all the unnecessary files.
3) Yes, definitely. Just follow the method linked above and your site will be running under a fresh copy on b2evolution.
4) Well, first than anything else, your hosting account needs to be reactivated. After that, and depending on which version of b2evolution are you running, to change the password directly in the database could be either easier or a bit more complicated. Please tell us your version to suggest a method. In any case, I think that use the site to change your password is just fine.