I purchased a mavic pro several weeks ago and want to put a 64 gig card in but I can't get the 16 gig card out.  Is something wrong with my mavic or is there a trick to getting the card to release?

For fear of stating the obvious, the card has to be pushed in slightly to eject it from the slot.    I don't have long finger nails so sometimes it is difficult for me.  I will sometimes use another SD card to help pushing this card in.  Just be careful that whatever you use not to slip it between the inserted card and the side of the slot itself.  Hope this helps.

A tip: Try blowing on the sd card. Then use your fingernail to take it out!

I finally got the card out by using my pocket knife and prying it out.  It was jammed.  When I put it back in it worked like it was supposed to.  Thanks for your help.

Had the same issue of having problem removing the card after a few insert  it seems like the spring back finally worked loose. Now have no issues.

Same here.  Not sure if brand new cards need to be 'trimmed' to fit better, or if it happens naturally by simply inserting/removing it a couple times.  Freaked me out when it happened, I thought the spring in the eject mechanism broke!  Nope, normal.