Water heaters are super easy if you can deal with the copper pipe work that is usually involved. Woke up to ours leaking years ago. Called into work, went and picked up a replacement unit and swapped it out and went in to work around noon.

I think our old one was a 45 gallon and when I replaced it I went to a 55 gallon and it was amazing how much longer you could take a hot shower before the water got cold. I had plenty of space to go bigger. Your mileage may vary.

Good luck.