Changing Your WordPress Theme

This should be obvious, but the more complicated your current theme is vs. your new theme, site design and formatting will likely go south. Be prepared for a redesign.

Similar to widgets, your theme may have post types. A very good example of this is a real estate theme. Your listings are likely created using post types for listings. Once you change themes, that formatting and content will go away.

Keep this in mind as I've seen many people who are not aware of this. Some of your widgets may be theme related and only exist when using that specific theme. Learn what they are and if you need to replace them, and you can hopefully find another general widget that will do its job.

If you have had any customizations to your theme, yes, they will go away. If had someone do them, hopefully you know what will be affected. Nothing worse than finding something that you thought could easily be replicated in your new theme turns into a huge challenge.

Typically, when you do change a theme, widgets will fly around into other widget areas or may drop into your unused widgets. In any case, if you have any text widgets set up with specific html, I would recommend copying and pasting them into a file. Just in case.