Personal Wireless

Hey there,
In our house we have comcast as our cable and internet provider. We have xfinity and it is supposed to power up to 10 devices but currently its struggling to provide for 2. Can i go out and but my own modem and router to supply my own internet? I apologize i am a bit new to this but getting fed up with terrible internet. Any suggestions are greatly appreciated.

Thanks,
Ozwald20