New to Company, Switching Subnets

I was just hired as a help desk tech at a small-ish company, knowing that the demands of the job were actually more jr sys admin stuff, and the employer hired me on knowing that there were some gaps in my knowledge related to the things I'd be doing. They were 100% totally cool with me learning new stuff on the job and helping to grow my skillset, but I've just been thrown a curveball that requires some faster reaction times than studying and testing can provide me.

​

We're currently on a 255.255.255.0 subnet and running out of space. We're going to be switching over to a VoIP phone system in the next week, and being that we currently have less than 25 available addresses left to us, we won't be able to accommodate IP phones. I was originally thinking about creating a VLAN for voice, since the phones we're getting have network pass through/VLAN capability.

​

However this was a super last minute decision decided on by the owner that kind of blind sided us and he wants to have it done by the middle of next week. Our systems analyst is currently building a new AD forest and creating a new network topology that includes separate VLANs for printers, user devices, guest network, etc, to go along with a massive server upgrade they're planning.

​

We've decided that with the time constraints we currently have, we'll just have the systems analyst implement another VLAN for the upgrades that are taking place three months from now, and we'll switch subnets and convert to a 254 subnet to get the available IP space for now. Being that there are only about 40 users, and they aren't on the phones all day, I don't foresee not having voice traffic on it's own VLAN with priority traffic becoming an issue.

​

I've been reading up on subnetting and have a much better general understanding now than I did yesterday, but that being said - I'm very much a hands on learner. I can read and get a okay enough understanding of a concept, but unless I have a clear, concise, step-by-step guide, applying the knowledge I've gotten from reading is a struggle. Especially when I didn't have a strong fundamental understanding of the concept to begin with. So I'm really just looking to confirm that I'm going about switching the subnets the correct way:

​

1. Change the network properties on the DHCP server (192.168.10.1) to reflect a 254 subnet instead of 255.
2. Change the settings on our Cisco switches to reflect the 254 change as well.
3. Any devices (servers, printers) with a static IP will need to have the subnet manually changed
4. ipconfig /release and /renew on user computers should pick up the new settings.

​

Am I missing anything here? Will changing the subnet on the DHCP server affect the handling of our reserved DHCP addresses at all aside from needing to update them on the device? Will I need to do anything with the DHCP management app? Any help would be greatly appreciated.