|Try recycling the power on your router. Unplug it, count to ten slowly and plug it back in and see if that doesn't improve things. If you have a separate modem, and recycling the power on the router doesn't fix the problem, try recycling the power on the modem.|
If neither fixes it, contact your ISP's support people as your modem may be having issues.
Also, your router could be having issues but check the modem first since most ISP's can remote into the modem and run some basic tests.
The only way to troubleshoot router issues is to get another one that you know works properly and use it for a while. If the problem goes away, it was your router. If not, it's something else.