Will changing the skin on my site hurt my site or change the content of the site?

You can change the skin on your site without losing any of the content of your site or harming your site.  
Please note that if you do change the skin on your site, any custom color settings you have set in Sites > [site name] > Skins > Customize Skin tab in the Customize Skin Colors section will be reset to the defaults when changing skins.  
If you are using one of our responsive skins, you can store the color palette before changing skins and then reapply the color palette to the new skin if it is also a responsive skin.  
Note : This feature is not available for our non-responsive skins.
Please go through this chapter for more information on Customizing Default Site Skins (latest)