My Rezound says "Error installing Instagram, there is insufficient space on the device." I went through my settings then to SD & Storage portion, and I still have 15 and 15 GB of SIM and SD card space and 2GB of internal. The application for Instagram is only 13.50MB. What the hell?
You may have used up all your temporary space, try going to Settings-Storage-Make More Space and tap "Temporary files from HTC Apps" and it should prompt you to clear out some stuff... You could also install ES Task Manager and run the Cache Cleaner to clear out cached items, there are other apps to do this as well.