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Back up your site
Regardless of your reasons for changing your WordPress theme, backing up your site is an extremely important step. This is a security feature that allows you to quickly return to the previous version of the website if something goes wrong. To perform a backup, you can use plugins such as UpdraftPlus, BackupBuddy, Whether Duplicator. For most of them, the backup process is simple and intuitive.
Make a note of any custom adjustments
If you have made any custom modifications to your current template, such as changes to the CSS, HTML, or PHP code, be sure to save these changes in a safe place. You'll probably want to move many of these customizations over to the new template.
Check plugin compatibility
Make sure the new template is compatible with the existing plugins on your site. Plugins may have specific template requirements and may not always work correctly with all of them. To check this, you can use a plugin like Theme Check.
Test the new template on a test server
Before you introduce a new template to your website, you should test it on a staging server. Thanks to this, you will be able to detect any problems without affecting the operation of the website. If you don't have a staging server, you can use a plugin like Duplicator which allows you to easily create a clone of your website.
Make SEO optimization
Remember that changing the template may affect the SEO optimization of your website. Therefore, before you make a change, check whether the new template is optimized for SEO and whether it will not negatively affect the website's ranking. You can use the Yoast SEO plugin for this purpose.
Run tests after changing the template
After introducing a new template, run tests on the website. Check that all elements look and work properly, and that the site is still accessible to users and search engines. A plug-in like Browser Shots will be useful here, as it allows you to see what the website looks like in different browsers.
Update the sitemap
The last step after changing the template should be updating the sitemap. This is important for SEO because it helps search engines understand the structure of your site. You can do this manually or use the Google XML Sitemaps plugin.
Remember that each change to the template is a big challenge for your website. Prepare properly for this and the process will go smoothly and without any problems.