Depends on the version of the 3300. Ver 7.1(?) allows you to set the IP.
System Config >>> IP Network Configuration >>> System IP Configuration.
If the system is older than that, you need to plug a serial cable into the front at 9600 baud and type bootChange.
Check out what your settings are by just hitting return through all of them and see what you need to change.
Bear in mind the subnet mask is in HEX.
If your PBX is handing out IP addresses to the phones, be sure to change the DHCP settings.
The YA may be even tougher since, if I remember right, you may need to get your licenses again from Mitel - not a big deal.
I have to say though, this isn't something I would expect a customer to do without dealer assistance.
Ralph