If you're using a preset, the resolution is part of the preset. Just change it. But, honestly, you won't see a difference between 240 and 300 in a print. Studies show that it's at 180 or below you can. Also there are a lot of print houses that do prints from 100ppi up. I've even printed 900X600 images from friends websites to demonstrate that they make acceptable (not amazing) 9X6 inch prints-yes, I gave them the prints.