Arthur Wright answered
In other words you want to get rid of the 3 way system and just go to 1 switch controlling the fan. Ok youre going to need to figure out which existing switch is your power side of the 3 way circuit, if this was wired right. Once and if you can get that figured out then you will use that power black to the power side of dimmer switch and use either the other black or red to the other part of the dimmer switch. Now on the other side cap the single black wire to the black or red coming from the same set of wires that you used on the other side and cap off. That completes your new dimmer/fan combo switch. Now if it has a seperate switch for the fan light and the fan itself , its going to get a little more complicated but can easily be done without any fire risk although not code but will work safely. Hopefully the wires in the box contain a ground thru it and cap off all grounds together in first box. Now in second box the red and black from the same set will be as follows black from the same set as red to black switch leg, red wire from the same set to the white from the 3 wire light set now the white from the black/red set ties to the switch copper wire. Now at the fan the black will be your fan dimmer control and ties to the fan black, the white bties to the blue from the fan as light and the white and copper from the fan attach to the copper wire coming up to light and all cap off. Install all switches and fan and it should work. Good luck