? on updating title of post. Finished!!!

I've noticed that some of the more savvy users (not me) of the site here can change the title of their post mid-thread

for example start off with a title

"1/48 Monogram B-25 WIP"

then go to

"1/48 Monogram B-25 WIP   UPDATE"

then

"Finished 1/48 Monogram B-25"

they can do this without starting a new thread (keeping all the previously posted pics, & replys)

I tried messing around on the test forum a little but couldn't figure it out.

Anyone know the trick?

thanks

Gary/1SG