reinstal wp theme with the same database

You can just deactivate the plugin there.

Depends on what broke when you installed the plugin.
Depends on what changes the plugin made.

I theory just uninstalling the plugin. Or simply deleting the plugin folder in wp-content/plugins/ should return your site back to it's pre plugin state.

However if the plugin altered files or database then that may not be the case. It shouldn't have altered system files but you don't say which plugin so I can't guarantee that.

If you have a wp backup from before the plugin break (and assume you have as you are talking about uploading them) then take a stepped approach.

1. ensure the errant plugin is removed. Delete the plugin folder. It will likely leave some database entries behind but at this stage don't worry about it.

If it is a broken theme then yes upload the theme folder/files in wp-content/themes. It may fix the issue.

You don't say what the issue is but if it's simply hanging or visually broken then try a logical approach to identify the core problem.

9 time out of ten it's plugins so rename the wp-content/plugins folder. If this fixes the break then create a new folder called plugins and move the plugins into that folder one a at time until it breaks again. You have then identified your problem.

If that does not fix it then try re-installing a new set of system files (from wp.org).

If that fails then maybe you have a database issue and you will need to install a backup of the database. How you do that depends on how you backed it up.