How to allow contributors to Upload Files in wordpress

How to allow contributors to Upload Files in wordpress? I allow my wordpress site’s contributors to submit posts. But by default, WordPress contributors do not have the capability to upload files. How to allow them to upload files?

The key to my solution to add the upload files capability to contributors in WordPress is the User Role Editor plugin: http://wordpress.org/plugins/user-role-editor/

For a detailed instruction of how to install the plugin and add the capability, please check this post: http://theitbros.com/allow-contributors-role-to-add-images-in-wordpress/

Also more details about the roles and capabilities in WordPress: http://codex.wordpress.org/Roles_and_Capabilities