when you get your IP address it is 'leased' for a preset time.
this is the IP that has been assigned from your ISP

if you wish to see IPconfig / release / renew at work, then you will need your own little network running

set the DHCP server to give IP's within your pre-selected range, and set the time scale low
NOW when you set IPconfig / release
it WILL release the IP address
and IPconfig / renew will get you a 'new' IP addy, or at least it 'may' assign you a different one fromt he range you have selected

[edit]
forgot to add

when you release / renew the IP addy from your ISP
it DOES release / renew the IP, it just re-assigns the one you had.

best way to get a new IP
log off for a couple of days, then log in
the chances are then better that the IP you have 'leased' will have expired, and a new one will be 'issued'