Will try and keep this as basic as possible.
- Download the database
- Download everything in the directory wp-content/
- Download wp-config.php
- Download .htaccess
Keep all of this safe and make a back up of it.
Install AMPPS this will give you a web server on your local machine.
Set up a new domain from http://localhost/ampps use something like dev.youdomain.com
Then inside AMPPS/www/dev.youdomain.com put a new copy of WordPress
Copy in the contents of the directory wp-content/
Add your new theme to wp-content/themes/
Open up your database with something like Sublime Text and do a find and replace for;
Replace All: http://dev.yourdomain.com
Now create a new database with AMPPS at http://localhost/phpmyadmin via the PHPMyAdmin interface.
You then need to import your amended database into the one you created.
Assuming the database isn't massive then this shouldn't be a problem. If it is then you'll need to increase the file upload size in the PHP settings. This is a manual process by editing /Applications/AMPPS/php-5.6/etc/php.ini
Change max_execution_time, max_input_time, post_max_size & upload_max_filesize to the following
max_execution_time = 300
max_input_time = 600
post_max_size = 1024M
upload_max_filesize = 1024M
If you change any of these then restart Apache.
Edit the database details to match what you've just set up in PHPMyAdmin
(In AMPPS: username is root, password is mysql)
Visit: https://dev.youdomain.com in your browser and run through the normal install instructions for WordPress.
SECURITY TIP: Do not use Admin as the default admin username!
Then go to
Dashboard > Appearance > Themes
Enable your new theme here
Then go to
Dashboard > Plugins
Check that all of the plugins which are running on the live site are enabled here.
Visit: https://dev.youdomain.com and see how it looks, then tweak the theme to fit your needs. You might need to double check the old theme doesn't have any custom code included in the templates to display parts of the existing site.
Remember if you amend an off the shelf theme downloaded from WordPress or elsewhere then you won't be able to update it in the future. The easy way around this it to make a child theme, or better still a custom theme from scratch.
I'd strongly advise you take a look at this if you plan to have development, staging and production environments running https://github.com/studio24/wordpress-multi-env-config
Personally I would also consider doing a content audit of your site. Content which was relevant 2 years ago may no longer be.
Examples, you may have content littered throughout your site like so
"Happy Christmas from all of our team"
"Please contact Jenny Smith for the latest information"
"The retail price is £39.99"
All of this is likely to be no longer required as it's April, Jenny left and the price is now £49.99.