try this...

Assume the manual is:
http://www.tenda.cn/uploadfile/downloads/uploadfile/201204/A5-EN.zip

Your Cisco router's inside IP address: 192.168.0.1

1. (Page 30) Change it to, say 192.168.0.2 (you may need to do something in your Cisco router, but let's try not to first)
(Do not forget what's the IPs you've changed from and to!!!)

You probably need to re-login again to 192.168.0.2 (your Tenda's new IP address)

2. (Page 43) Disable DHCP