Multiple where

Hi all trying to put together a script, I took the follwoing from Virtu Al and this works but for one set of variables, For the life of me I cant get this to work if I add an if or elseif statement 

$OldNetwork = "PG1 192.168.0" 
$NewNetwork = "PG2 10.1.1"

Get-VM |Get-NetworkAdapter |Where {$_.NetworkName -eq $OldNetwork} |Set-NetworkAdapter -NetworkName $NewNetwork -Confirm:$false

what I would like is something like 

$OldNetwork1 = "PG1 192.168.0" 
$NewNetwork1= "PG2 10.1.1"

$OldNetwork2 = "PG10" 
$NewNetwork2= "PG2 "

so if the first "where" statement wouldn't match it would go on and try to match another portgroup.  Any help much appreciated tired of seeing red

thanks