Leave IP the same but change subnet.

Hello Thwack Community!

I have a quick question for you all; How would I go about changing the subnet mask on a VLAN but keeping the individual IPs the same while utilizing NCM?

Example:

192.168.1.2 255.255.255.0

192.168.1.3 255.255.255.0

to

192.168.1.2.255.255.254.0

192.168.1.2 255.255.254.0

Thanks in advance!