It will be written in green right next to the word report.
The bottom left side will read Report Edit Delete
However there is a time limit for editing because the forum archives after which the edit vanishes
But you can still delete for quite some times then repost >
I have needed to do it a couple of times when what I posted was shown to be wrong.
What might be happening is your device is not downloading the actual page from the server but using a cahed copy
If you are using a computer do a forced reload ( google for your devices method ) as soon as you post and see if the edit turns up strait away.