Wrote a comment on Facebook and regretted it. If it is on your timeline or you wrote on someone else’s post then you can do it. Just go into comments on the post click on your comment and you should get a choice to Reply, Edit, Copy or Delete. So you can adjust it with Edit, handy if you have made a spelling mistake, or get rid of it with Delete.
Or if you need to adjust a post, go to the post on your timeline and you will see three dots on the right top of the post. Click on the three dots and you will have an Edit and Delete function there as well.