What should i do with my backup receivers?

I have Miles Austin and Pierre Garcon as my backups for my fantasy team but both are still unproven. Should i trade them or keep them? If I should trade them, for who should i? I need a really good running back. My other starting receivers are Donald Driver, Jerrico Cotchery, and Derrick Mason. My RBs are Ryan Grant, Pierrre Thomas and LeSean McCoy.