My current modem is a modem/router combination. It's not great so I wanted to upgrade to TP Link. I also don't get internet in one part of my house so I bought an extender.

I set up the new TP link router as a router and then also an extender. However, again, there was no way to turn off the old network because the modem is also a router. It was pretty good but sometimes would be slow, and I felt maybe the networks were fighting with each other. 

Setting up the new TP link router as an Access Point instead seemed to be a good solution. Now they would work together and not fight. I then went to set up the TP extender, but it will not allow me to mesh networks. Can I only mesh networks if the router is set up as a router?