Welcome to the forum, and to the DFRPG! Awesome to see new posters, and hope you like it here
After a session, is the GM supposed to give 6 refresh or is it supposed to be the adjusted refresh of 1?
Actually neither. At a refresh (usually at the end of a session, yes) you get Fate Points
up to your Adjusted Refresh. If your adjusted refresh is 4 and you have 2 FP at the end of the session, you get 2 more (so you're at your refresh of 4). If you instead have 5 FP, you don't get any new, so spend those FPs! This also means that if you have an adjusted refresh of 1 (quite common for Wizards, for instance) you'll actually only get FP from the end-of-session refresh if you're empty!
Then, for a Minor Milestone, I can't can't take on any more powers/stunts because my adjusted refresh is 1 but I could switch the powers/stunts that I have for new ones?
Almost exactly right! You can't by default switch out Powers; everything else is correct. Of course, there's always special cases where the story warrants switching powers, but usually that'd be a pretty big deal and probably not happen in the "off camera" moment that taking the refresh signifies.
Hope this helps clear things up!