Hey, If you want to upload and edit your blogger template then you must need to make your blogger template backup before doing any change.
It doesn't matter if you are uploading or editing because every time you need to keep yourself site on the safe side so it's mandatory to make blogger template backup while doing any change and uploading.
If anything happens while doing any changes on template or uploading you can use a previously downloaded template on your site. That will definitely gonna help you because that template is already configured for you.
Sometimes while editing blogger template there may arise problems with codes, so you need to be careful and you have to keep yourself at safe side. If any problem arises with the new template you can upload backup downloaded template.