downgrading edition from Enterprise to Standard is not officially supported directly, but...
Note: First you need to stop the service
This is the procedure from the client side (before I had enterprise and I change it to standards) :
as far as I understand this execute behind the scenes a full uninstall and then installation of the lower edition
Update: Here I found the official documentation. You can notice that changing from Enterprise to Standard is not supported (not in the list) but it is working according to my tests as I show above (with the understanding that this is an uninstall + re-install procedure), but moving from Evaluation Enterprise to Standards is supported (which is why I find no reason to move from Enterprise as well but do it on your own responsibility).