If you are setup for permissions by the admin.
Under the body of the posting you will see:
Make this topic a sticky topic. check that and it is done.
After the fact the same rules apply as far as permissions. but changing a existing post is different.
Open the post in question.
Select the manage topic tab for a drop down list.
Elect the:
Make this topic sticky.
If that option does not appear then you need to request to have your permissions changed.
