Go to Resources.
Select the Resources tool from the Tool Menu of your site.
Select Actions, and then select Edit Folder Permissions.
To grant uploading permission to group members, select Edit Folder Permissions from the Actions drop-down menu to the right of the group folder.
This displays the folder permissions.
Note: You will need to make the folder a group folder in order to limit uploading permissions to a single group.
Modify student permissions and then Save.
In the student column, select Create resources, Edit own resources, Delete own resources, and Access/create group resources, then click Save.
This allows the students that are members of the group to upload and edit content in the group folder. Students that are members of the group will have an "Add" section available in the folder's Actions drop-down menu.