How do I change to alternate team jerseys in season mode?

Exactly what the title says. I am trying to change my team's jerseys in season mode to their alternates. How am I supposed to do that? I went to the settings menu, then I tapped on the "Change Uniform" option, but it won't let me change the uniforms (the arrows to toggle between jerseys are there, but they are grey and nothing happens when I touch them.) How do I switch between jerseys?