To change what themes are available network wide:

1. Click on Network Admin link in the top right of the WordPress Admin to access the Network Admin dashboard.

2. Click on Themes in the Network Admin dashboard area.

3.  Select the themes you want to make available to all sites by either:

• Clicking on Network Enable below the theme name
• Or selecting all themes you want to enable, then select Network Enable from the Bulk Actions drop down menu and click Apply

Once enabled the themes will be made available for use by site admin users and be listed in Appearance > Themes in the Site Admin dashboard.

See Next:
Changing what themes are available on a per site basis