html5syt When you say plug-ins, are you referring to extensions? If yes, then they can either be disabled in your Admin area by selecting the disable toggle or uninstalled by going to your Flarum directory via cdand typing composer remove COMPOSER_PACKAGE_NAME.
There are default extensions though that are part of the Flarum core like Approval, Likes, Mentions, etc. You can disable them but I’m not sure if you can uninstall them. At the time of writing, there is no direct option to uninstall additional extensions from the Admin area.
I hope this answers your question.
