I found the old way to edit decks a bit complicated and unintuitive, so I have decided to change it a bit to hopefully make it much easier to use. So from now on, when you click "Edit Deck" on top of one of your saved decks, it will take you straight to the normal deck editor where you can change and analyze your deck as usual. When you are done, just press "Save Deck" to bring up the usual form. The old deck will be preselected under "Save As", so that you can just click "Save Deck" again to overwrite it with your changes.
If you just want to make small changes to your deck (e.g. update the description, add tags or change the format), you can now use the new button labeled "Update Details" to do just that. And if you want to make a copy of your deck, click "Copy Deck" under "Deck Tools" to bring up the same form as for editing, except when you save this deck it will be saved as a new deck by default.