It looks kind of like a coleman style. Have you taken the cover off of the center section to see what adjustment may be inside? If it is a coleman style, take the cover off and you should see the wiffle tree with four eyebolts (one for each corner) with adjustment nuts. You adjust the length of the eyebolts to adjust the height of each corner. You can also raise the roof to extended position and put equal-length supports at each corner so the roof is at equal height on all four corners and then adjust the eyebolts as needed to lift equally.
