Don't do that, it won't do anything for your sites in the network.
how can i change on (or all) of my sides to ssl? I can not change http:// to https://
Make a full backup of your database and files (it's the DB that's important) then using a search and replace utility modify all the HTTP urls to their HTTPS version.
Using WP-CLI it's as easy as
wp search-replace http://url-here https://url-here --network --dry-runThe --dry-run will give you a count before actually doing it. If you are happy with the count then run the same command without the --dry-run.
If something goes horrifically wrong then restore the database backup and you'll be where you were before.