As an administrator of your Facebook account, you are always able to delete an unwanted post, regardless of who posted on your behalf or when. However, posts that have been boosted with a paid advertisement (whether by us or by you) cannot be edited.
How to change the post
We use Facebook's Business Manager to set up ads, which we use for all of our clients and therefore cannot offer access to anyone but our staff. If you do require edits to a boosted post the most effective method is to send us an email to firstname.lastname@example.org with the details of the changes that you require.
If the nature of the change is time sensitive (i.e. an error that requires correction outside office hours), deleting the post will stop the paid advertisement as well.
Please, let us know if this is ever the case and we will repost a corrected ad for you as soon as possible.