The address that it hands out is determined by the DHCP server, which, in this case, is udhcpd. The configuration file for it is in /etc. Change the lease block setting at the very top of the file to your prefered values, then restart it at root (with sudo or su, or at the console). Here's how to restart it, with "#" being the prompt.
# /etc/init.d/udhcpd restart
Best wishes,
Bob