Hi Benji, your content (if you mean pages, posts etc and the content within them) is independent of the theme so it will not be affected when you switch theme.
If you mean the theme customizations you have made to the Exoplanet theme, then Exoplanet Pro has ‘Theme Mods’ option in the dashboard (just above the ‘Appearance’ link).
In Theme Mods simply click the ‘Import From Exoplanet’ button and your Exoplanet theme customizations will be copied into Exoplanet Pro.