It is not that hard, if your tank has a drain plug it would be wise to drain whatever fuel is still in the tank. If no drain plug get a pan of some sort to catch the fuel that will come out when you release the tension.
A brass drift pin or punch is best, something that will not spark when hit with a steel hammer. In a pinch a piece of wood might work. The collar around the sending unit unscrews, use light taps to get it started. It is the standard right hand thread, be sure your hitting it in the correct direction. A few taps should get it started and then it will unscrew fairly easily.
I hope that you have a new O-ring for the replacement sender, I used a little vaseline to help hold it in position. Installation is the reverse of removal.
I need to do this on my 68, and I don't remember from the last time - but does it line up only one way? When I replaced it many years ago it never would read "full", but only 3/4. Does it need to be rotated or was the sender faulty? It doesn't work at all now, so I am replacing it anyway.