Booster (WiFi repeater) could improve WiFi radio signal in hard to reach areas of the house. It amplifies and retransmits all radio signal (within WiFi frequency range) it receives. You'll have to find a good spot for it, somewhere between your router and target destination, so it can still get decent signal from both locations. It's not my preferred solution, however.
You could also pull an Ethernet cable from your bedroom router to remote area of your house and connect a cheap WiFi router/access point to the other side.
If pulling a cable is not an option, you could buy and use a pair of PowerLine adapters instead of the cable.