Petbro is bang on.
But I will add this - find what is comfy for you I was told always to keep my thomb at the back of the neck, but it did not suite me so I play with my thumb sort of around and over, works for me but not for every one else.
Try all way's.
We all start out with the same problems and we all practice and overcome then something else comes along for us to overcome.
once you overcome a problem you think to yourself god it wasn't that hard and grin to think you were daft enough to let it get you worked up and feel down as to how far you are progressing.
Once you learn to overcome one type of problem like chord changing it gets easier to overcome the next challenge such as soloing or sweep picking or what ever.
the guitar never gets easier you just get better at achieving thing's on it and moving on to the next stage.
*Never think what you cant do*, look back at what you can do. think I learn't the chords so I must be able to learn the changes.
While I'm sat here, Playin', I'm tryin' to free my mind!