If you have another client on the LAN, see if you're getting horrid LAN speeds. Also, if you have another client on the LAN, make sure they're not using the internet connection, when you're saying that it's slow.
You can try rebooting the router, but I highly doubt that's your problem. Run some speed tests
like this one, and come back with some specific information (ex: my line speed is rated at xxxx/xxx, I used to clock it at xxxx/xxx, and now it clocks at xxxx/xxx, I'm the only client on the internet connection, I'm using Windows XX, I'm using XXXX NIC, and model XXX router/AP.)