Usually updating a software means replacing the old files with the new ones, but there is a better way to do it when it comes to WordPress themes.
WordPress treats two version of the same theme as different themes. That is, if you have SWIFT v5.1 and v5.1.1 in your wp-content/themes folder they are treated as two different themes independent of each other.
That means you can have multiple version of the same theme installed on your blog. So whenever there is a new version of your theme available, instead of replacing or deleting the files of the older version follow this procedure.
- Download the new version of the theme onto your computer.
- If the folder name of the new version clashes with the old version, rename the folder of new version.
- Upload the new version to your wp-content/themes folder via FTP or through the interface provided by your web host or by using the upload feature in WordPress.
- Activate the new version from your dashboard.
The main advantage of following the above procedure is you can quickly switch back to the old version of the theme if you find any problems with the new version or if it clashes with any plugins you are using.