Technicolor Router IP 10.0.0.138 option?

[#1]

I have a Technicolor TG582n as supplied by PlusNet, and this gives me full speed 70/15 Mbps.. great.. amazing!. But it seems to be fixed at 192.168.1.* IP range. Well I have tried to change it to 10.0.0.138 without getting a succesful config. My old Linksys WAG320N has gigabit ports which suits my Cat6 wired house and connects using Ethernet port 1 as WAN but that throttles me down to 27 Kbps downstream. I have a NAS setup, SMTP server, a wiki server, and web server, TV, Video and Media player, VPN ... all nicely set up on 10.0.0.x with NAT options.
So - can I get the Technicolor to operate OK on 10.0.0.138? Having a 10/100 port for the outside world is fine as 100 Ethernet is faster than the Fibre. And I have a gigabit bridge that can link all my internal Cat6. But I do need to get the main router to deliver both the fibre speed and the 10.0.0.138 default gateway and 10.0 DHCP.
I suppose I could buy a new router, and I guess this is > £100.
Any suggestions?

[#2]

By default the TG582n has 2 IP addresses allocated 10.0.0.138 and 192.168.1.254 together with a DHCP pool on the 192.168.1.x subnet, with a default gateway of 192.168.1.254. To change the DHCP pool you need to disable DHCP first, change the pool and then reenable DHCP. You might find this thread http://community.plus.net/forum/index.php/topic,110846.0.html useful.
Hope that helps