Not sure--did you already pitch your yeast or not? If you pitched at 74F you should be fine as far as not killing the yeast. However, depending on the strain you used, you may still want to cool it down, since many yeasts ferment best in the mid-to-high 60's. If you ferment at a higher temp than the yeasts prefer, they'll get stressed and produce off-flavors in the beer. It probably won't ruin it, but you can get a cleaner, better tasting beer by keeping your temps lower. Check on the yeast maker's website, they post optimal temp ranges for all of their individual yeast strains.