The instructions below are for bulk applying a package to multiple galleries.
1. Navigate to the Library > Galleries area.
2. Select the galleries. The tutorial in this link will walk you through the different ways of selecting the galleries.
3. Once the galleries have been selected, the bulk edit tool appears. The next step is to choose a package from the dropbox and click the Apply button.
NOTE: If the 'Choose a Package' box doesn't appear, then you probably don't have a package set up yet. The tutorial in this link will walk you through the steps required to create a package.