Assuming you are using the 7762 in Standalone mode, SSH into the AP and use the following command :
rkscli: set qos directedDHCP disable
Direcet DHCP is Disabled
OK
PS: you can use any SSH client, eg. PuTTy - can be downloaded from
http://www.putty.org/ for Windows. For MAC OS just use your terminal to SSH.
Hope this helps, cheers!