I would plan to change only one tire at a time. It's going to take longer than you expect, especially if this is your first time doing this.
plan for X amount of hours, budget for double that.
to make installing the new tires easier, heat them outside in the sun, first... the longer the better... hours, if you can plan it that way, to make them more pliable to work with when it comes time to actually install them.
double check, when you get ready to install the tire on the rim, that you have the tire orientated in the proper rotational direction. It's a bitch to completely mount the tire and then find out you've installed it backwards. Ask me how I know!!!
gl... take your time and have fun.
