Sharpen Entire Images
Sharpening an image is a common photo edit, but that option is a bit hard to find in iPhoto for iOS. Tap the Brushes tool and then select the Sharpen brush. It's designed to let you sharpen specific areas on which you paint the adjustment, but that approach isn't helpful if you want to increase the sharpness of the entire image.
But it is possible: Tap the Settings button (the gear icon) and then tap the Sharpen Entire Image button. You can then change the level of sharpening (Low, Medium, High) and it will affect the full photo.