WIFI issues with my iMac Yosemite 10.10.5

I have a mid 2007 iMac that is running on Yosemite 10.10.5 4GB Intel ..and we have two routers in our home. The problem I am having it keeps searching between the two and my systems runs like I have dial up. This all started when I downloaded 10.10.5 and we got the 2nd router in the house. I got my own router because there were just to many of us running off the first one....Help please ...I feel like I am back in the 90's with AOL.....