I've never done it myself. I know some people spray paint them, but I prefer to leave it to a professional. I get all mine dyed at a local shoe maker/repair shop. I leave them the pants to match the color and they've always done a wonderful job. Just call some local shoe places and see if they do custom dying!
I use car paint in spray cans. The car paint is great and doesn't chip/peel easily since it is meant to conform to the body lines and curves on a surface. Some people prep the surface by stripping the finish, roughing it up etc. I did no prep on my boots, just taped the soles, painted and sealed. I am not crafty or handy in any way and did this with no problems. I refinished them last year just to give them the bright "new" look, but they weren't peeling/cracking/chipping. I wore them lots for 3 years before I thought they needed a freshen up coat.
If you're a size 7-7.5, mine are for sale (teal). They didn't fit the girl that bought my showmanship and are nice flat sole square toes. :)
Really easy to mess the finish up on your boots doing this at home. I would take it to a tack shop and have someone do it professionally, they also are able to match the colors a lot better than you can with a bottle of spray paint. There's a lot of things that could go wrong.