DHCP - expand network IP addresss

In the scope properties

set the start ip address and end ip address

change the subnet mask

What is your original subnet ?

192.168.156.x/24

I went in there and saw where to do that but the subnet mask is greayed out

Yes that is correct you can not change after your create the scope.

Create a new scope

with a mask bit of 22   this will give you 1022 addresses

You might want to use 10.1.8.1/22

ok. why use a class a?

I currently have 192.168.156.x/24.. so I should be ok if I user 192.168.156.x/22 right? and I anm not using .157 anywhere.

You can use that but I would look at this first.

http://serverfault.com/questions/591104/i-need-more-ip-addresses-can-i-change-my-mask-from-192-168-x-0-24-to-16-why-n

This is a subnet online calculator and your 192.168.156.0/22 is really not valid  take a look.
http://www.subnet-calculator.com/subnet.php?net_class=B

I know changing ip address is a problem with all the static addresses etc.

But if you need more addresses I would suggest a valid address

We use cidr now not classes

thank you