I know there has been a few comments about how to delete clients in the DHCP list, but none really tell you how to do it, so here is what i did to get rid of them.
Download WinSCP and install
Log in to the advanced section of the router under root and go to processes and terminate the following process;
Log in using WinSCP, making sure that you select SCP in the very top drop down box. input 192.168.8.1 and the root password.
Once logged in, in the right pane, go to the following directories and delete the files;
/etc/tertf, delete the file: tertfinfo_bak, and
/temp/tertf, delete the files tertfinfo_bak and tertfinfo
Sync those two directories and then reboot your router. The router will then input new files and they are clean of all devices.
Worked for me
Or just factory reset, might be easier