Did you use the pre-configured SD card image? If so, there is a program called ‘select_program’ in the home folder that you can run to choose which program you want to set as default. You will need to run this in command line. If you didn’t use the pre-configured SD card image, you should check the instructions of each program to see how to uninstall it:
Dan’s interval_program: http://rayshobby.net/mediawiki/index.php?title=Python_Interval_Program_for_OSPi#An_alternate_method:
Rich’s sprinklers_pi program: https://github.com/rszimm/sprinklers_pi/wiki/Installation