Being a WordPress user, due to availability of tons of themes, one might get desperate to change his/her theme now and then. Changing the theme, changes the structure of that WordPress site, and this might be a bad sign for SEO since continuously changing the theme ultimately makes the search giants like Google & Bing think that you are not serious about your site.
Besides SEO there are also other few things which you might consider before changing the theme of your WordPress site.
Backup previous themeChanging your WordPress theme isn’t dangerous since you can switch back to previous theme anytime you want. But it is wise to regularly backup your WordPress site, because nobody knows when you might face data loss due to accidental errors and bugs.
Check menu placementsSometimes Menus might get hidden while changing the theme. In that case you can quickly assign menus to the new theme by visiting Appearance > Menu and select appropriate locations in the new theme for your menus.
Custom Post TypesSome WordPress theme makes use of custom post types which might not be supported by other themes, as a result you might see your site content not being rendered correctly. In that case you might want to make use of plugins such as Post Type Plugin which changes Page to Post, Post to Page, Page to Attachment and Post to Custom. Or simply you can switch back to the old theme to copy the content into the new one.
Platform IndependentCheck if the new theme works perfectly on all the modern browsers and devices.
Theme SourceNever make use of nulled WordPress themes. Tons of premium WordPress themes are available for free to download from unreliable sites. These sites place encrypted codes into the theme files, and eventually your site might get hacked and fall into wrong hands. Always use WordPress theme either from WordPress theme repository or from reliable sources like Themeforest, StudioPress, etc.
Bonus Tip: It is always wise and safe to to test the new theme in your localhost and if everything works fine just as you wanted, you can then apply it to the live site.