Center Content in Skins
In each Skin you can edit the Media, Cover, Overlays and Content parts. Overlays and Covers appears over the media till the content which is always visible can be shown above and/or below the Media.
The Content is left aligned by default, however you can set this attribute under the Skin layout Settings like shown in the following image:
Here you can set the Content to be shown above or below the Media and if the default align of text on the container should go to left/center or right.
Once you centered the Text, all content within this page (which has no left floating extra) will be centered: