Changing Frequency of baby monitor.

I operate a sanctuary for abused horses. There are 2 barns on my
property. One is the "hospital" for horses that are seriously ill.
The other is for those who are relatively healthy but need to be
indoors. There are times when I need to monitor the barn or one
particular horse. When weather is bad, I cant keep going to the barn
every hour or so, and I cant "camp" in the barn. While a video system
seemed like the solution, I found the cost prohibitive. Instead I
picked up two used Baby Monitors and placed the transmitters in each
barn, and tuned in my police monitor to receive them.

This works fairly well, and I can listen to the horses. Their sounds
do tell me what is going on most of the time. However there's one
problem. Both transmitters are on the same frequency. This means
that I have to go to the barn I want to listen to, and plug in the
transmitter, and then unplug the other one. Thi rather defeats the
purpose. Each needs to be on a different frequency.

I have some electronics background as a hobbiest, but I am not all
that familiar with these baby monitors.

George

Is there a way to change the frequency on one transmitter?