You can update (yourself) the summary (I.E. title) of trac tickets.
Trac ticket descriptions can only be edited by trac admins or people with ticket modify permissions.
That said, we do not encourage the modification of either forum posts or any other posted content, and lately have clarified the rules around this (particularly for the forum) as frankly it's been getting out of hand.
The core devs do sometimes read this and *may* agree to do something depending on the issue, but I can't promise anything.