Why the router works slower when connected to many PCs

My current network configuration is as follows:
INTERNET==>ROUTER==>SWITCH==>PCs
I’ve noticed that the router’s performing well and I’ve to restart it 4 or 5 times a day to increase its performance specially the wireless connection which fails.
all the PCs connected through the switch are using static IPs, only the wireless PCs are using the DHCP function in the router
can buying a new router solve this problem, all I’ll have to change the network configuration to stop the router from hanging