In Group Navigation, click the Files link.
Once you click the Files navigation link, you will see where all the files are located for the group.
Click the Upload button to add new files to the group.
Find the file you want to upload to the group. Click the Open button once to upload the file.
Once you upload the file you selected, it will show up in the Files section of the group navigation. This way all the group members will be able to access the file.