We had this same problem with our family tent (6 person tent) while camping in the interior of British Columbia. And it gets hot there.
First of all, color maybe beneficial for you. Try choosing a tent of a light color such as off white or cream. Light colored fabrics tend not to get as hot as dark colored ones.
If a tent has flap window with the ability of being tied open (which ours did) on the sides where there is no door this would be helpful in letting the air circulate in and out of the tent. However if your tent has these features, but has a sort of screen sown into it in order to keep the bugs out, then the open windows are really of no avail. And if possible keep the door open as well.
Other than this I would suggest tenting in the shade if possible or making some shade with a tarp to keep the sun off the tent.