Changing Technicolor TG582 to a different Subnet -192.168.1.254 to 192.168.252.2

[#1]

Hello,
I'm looking to change the subnet of my Technicolor TG582 router to something different compared to my VPN as it will not otherwise work. I have struggled to find any information on how to do it. Also, as most devices in the house are allocated IP's by DHCP (some even don't have the ability to store a static IP), I'd like to please know how to change my router from 192.168.1.254 to 192.168.252.250 - i'm using a random IP but crucially, I would like the last two (is it Octets??) to be three digits long. The subject is missing these two last digits as the subject is limited in characters.
Also, how do I update the DHCP accordingly?
Please could you explain it to me as a router newbie? I had read somewhere that I might need to download the config file, I have it open on my laptop but I was hoping that there'd be an easier way - is it even a "right" way to edit this file to secure an altered DHCP Pool and Subnet for the router IP? In any event I found it stumping!!
Could somebody please kindly take me through it and, if necessary, let me know exactly what to and what not to edit in that file?
Many thanks
Kind Regards,
plusbg.

[#2]

Save the original config file first. Then edit it, changing everywhere you see 192.168.1 to 192.168.252 leaving all the final octet values as they were.
That will change your subnet, router IP and DHCP pool to a 192.168.252 subnet.
Reload the new config file and your router IP will now be 192.168.252.254 and it should allocate DHCP addresses in the 192.168.252.x range. You will need to release & renew the DHCP address on any device connected to it.
If anything goes wrong then factory reset it and reload the original config file...

[#3]

Thanks - this worked a charm!!
Anybody else following this - once the file appears to have stopped loading, give it another 2 mins to be on the safe side, then, for this to work, you must turn off the Technicolor TG582 and then turn it back on - then, you're good to go - otherwise, you will think it has not worked 🙂
Thanks so much - issue sorted!!