WNDR4000 Speed Issues

I upgraded my internet service with my ISP because we needed our internet faster since I started working from home. However, we saw no difference in download speed when conducting speed tests. My ISP assured us that there was nothing wrong on their end as they had just made another upgrade about a week ago and they replaced a modem recently as well. This leads me to believe that there is something that the router is bottlenecking as speeds reflect a much slower speed than it should be. Plugging into the router via Ethernet cable gives my computer the appropriate speed but any wireless device does not reflect the same. I know the speeds won't be the same between wired and wireless but the speed that the wireless devices are running at are abysmal. Do we need to upgrade the router? Is there something else I can do inside routerlogin.net? What options are available? Thank you for your help.