Hi Robert,
This can be done a few ways :) The simplest is to find the DN's in question and and just switch them on the proper DN configuration page. For example, let's say you want to switch 5555 and 4444. The first thing to identify is is the phone mac for each DN via> Device > Phone > search > based on Directory number (5555 then 4444 respectively)
So your search yields;
5555 = mac AAABBBCCCDDD
and
4444 = mac DDDAAABBBCCC
Go to AAABBBCCCDDD and change the DN config page to 4444 (check name display forwarding, css etc.)
Go to DDDAAABBBCCC and change the DN config page to 5555 (check name display forwarding, css etc.)
Update >reset > Test
Hope this helps!
Rob