Tim:
If the device is sitting on its original 192.168.1.1 IP and you need to get into it to change it to the IP you want (192.168.8.1), then change your PCs IP to one in the same range (e.g. 192.168.1.107), log into the device, reconfigure it, restart it, then change your PC's IP back to your desired address.
Marco Moock:
I don't see any reason to change that in this case. The "server" can be reached by http, should be enough from the networking side. :-)
It will depend on the networking configuration (or netmasking, in this case) on both sides.
Sometimes a device on something like 192.168.1.1 *can* talk to something on 192.168.8.1 directly, sometimes traffic will be blocked.
If the netmasking is 255.255.0.0 on both sides, I'd expect it to work. If either side has 255.255.255.0 it may not. Some devices are strict about rules, some try to be helpful. I remember a friend's modem/router being the very opposite of a firewall, it automatically tried to route any and all traffic through it.
I've had this palaver before when I've had to connect hardware devices to a network. We had some devices that just had to be on 192.168.1, because the manufacturer was pig-headed. It forced a renumbering of the entire LAN. Then I changed modem/routers and it came preconfigured for 192.168.0, fortunately it could be changed. I'm glad I didn't have other hardware devices that could only work on 192.168.0 at the same time.
I am seeing a similar thing now, here. I'm using a mobile phone to access the internet for my LAN, it insists on a 192.168.42 network (and I wouldn't be surprised if it only allows throughput from devices it's assigned IPs to, itself - interlinking DHCP with access control). It's certainly a pain in only allowing 10 devices to go through it. To use that addressing would mean renumbering my whole LAN, and then making my LAN unusable when the phone is disconnected. Or putting a PC in the middle to manage things.