Can I swap 2 8OHM subs for 2 4OHM subs and keep the wiring the same? and What are OHM's?

 

Nope. Since you already have 2 8 ohm subs Im assuming they are parallel wired and thrown on a bridged 2 channel amp.?

Ohms are like resistance. The more ohms, the more resistance, and amps are only stable down to so few ohms, so its important to keep that in mind when looking for a sub/amp