Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
You can't do anything to boost the output of the modem itself, that is a limitation of its internal antenna and power supply.What you can do however is to use a wifi extender/booster as separate equipment. Or, preferably (if your roku model has an ethernet port on it) use a powerline extender.
Here are 2 recommended options for this -
Booster/extender: http://amzn.to/1GJpKckPowerline extender: http://amzn.to/1RBB5vC