How to apply, edit or delete (manage) labels in Blogger/Blogspot

How to add/create labels in blogger?

To create a label while writing the blog post, simply click Labels under Post settings and start typing the labels separated by comma (,).  This way, you can create multiple labels at the same time. Later on you can simply remove the labels from the post.

To apply existing label, edit the post and write the same label in the Labels box. Or select the post in the posts manager and then click on Label icon then select the label.

How to edit (change/rename) a label?

To change or edit a label, first select all the posts containing that label, by selecting All Labels menu in the dashboard upper right corner. All the posts with that specific labels will show up in the dashboard.
Select all the posts.
Now create a new label and apply, the label that you actually want to rename to. Then apply this label.
Finally, select all the posts and then just reapply old label which will actually delete it.