I'm a new brewmaster but I recently tackled this issue. I brew in the desert, it gets warm here.
Get a bucket large enough to hold your fermentor. Fill bucket with water up to, or below, the level of the beer in your fermentor. Cover the fermentor with an old, wet t-shirt dangling in the water. It works reasonably well, keeping temperature below ambient, especially if you add bottles of frozen water to your bucket.
Another option is to look up plans and construct your own fermentation chiller. Look up "son of a fermentation chiller" or "mother of a fermentation chiller" for a good starting point.