3
To expand on what Stefan88 said:
1. Go to Admin>System>Modules
2. Select (use the checkbox) those modules that you wish to remove. Hitting "Select" with "deactivate" them
3. Once "deactivated" they can be uninstalled using the icon on the right. Uninstalling removs the module's tables from the database.
4. The module will now be in the "uninstalled list" at the bottom of the modules page.
You can then remove the modules files from your server.
Search on this site for the "Operations Guide" - it will help you in managing your modules (and site more generally).
HTH