Take out the valve core and heat the tire and let it sit without the valve core at room temp and check the tire. If your using a hot box I would heat at 150-175 for about 10 min and check. You can use the oven but it's not the safest thing so I won't go into detail but I'm sure someone will explain that also.
Some like to squeeze all the air out of the tire once the tire is hot, replace the valve core or use the cap and then submerge the tire in ice cold water with ice for about 10 min.
Again I like to just leave the valve core out and let it cool to room temp. You may have to repeat...
to use the oven, you take out the valve core, preheat oven to 300 and put the tire in the oven with the edge of the rim laying on the rack, not the tire. Leave tire in the oven for 5-10 mins, take it out and let it cool to room temp, then air up and check size, repeat as neccesary. Some will do like said above and squeeze the air out of the tire while hot, then replace valve stem or put a cap on it and stick the tire in ice water for 10-15 mins. What i like to do is take the tire out of the oven, put a piece of fuel line over the valve stem, squeeze out all the air and stick the tire in ice cold water while keeping the open end of the fuel line out of the water so no water gets in the tire, leave in the water for 15 mins, then remove tire, let it sit to get it to room temp, then air up and check size, repeat as needed. Putting the tire in ice cold water helps to shock the tire to help it keep the size you want it at for longer. Sometimes if you just heat the tire then let it cool naturally, the tire doesnt like to keep its size too well. Thats been my experience with burris tires.
( DO NOT PUT A TIRE IN THE OVEN THAT YOUR WIFE COOKS IN IF THAT TIRE HAS PREP INSIDE, IT CAN CAUSE THE OVEN TO REEK OF PREP AND TAKES A LONG TIME TO GET THE SMELL OUT OF THE OVEN AND OUT OF THE HOUSE!!!) BEST WAY TO USE THE OVEN TRICK IS TO BUY AN OLD OVEN SOMEWHERE AND PUT IT IN YOUR GARAGE FOR ONLY SIZING TIRES WITH!!