@Sleepy_Mechy 

Have you tested the speeds with another device?

It could be the PC. One thing that can happen is the PC could have no or unusual WIFI if you changed routers and used the same SSID as a previous router. You can try deleting (forget) the WIFI network on the PC and reestablishing it.

Also check any settings that your network adapter has as well as check for any updates for it.

On the router side, be sure the firmware is up to date, you are using the power adapter that came with it, the antennas are installed correctly, the router has some space around it and not up against another electronic device, try different channels and bandwidths. If still no go, try a factory reset.