Currently in GTR, once the step collection has been created, the only option is to delete it, it can not be modified after creation. In order to edit a collection, you must start a new job, add the collection, make your edits, save it as something similar to the existing collection, then run it on one or more assets, for it to save. Then you must go back into Manage step collections and delete the existing collection.
The only work around I have found, to be able to save using the current step collection name, is to open GTR in another browser. Create new job, add existing step collection, then go into other browser window and delete the original Step Collection. Then you can save the new collection with the existing name.
This could all be prevented it there was an ability to edit step collections under "Manage Step Collections"