To Update theme, Premium theme or Plugin manually without losing or deleting previous Version of the Plugin or theme. Read up this blog post.
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Login to your wordpress dashboard backend, goto plugin and add new plugin
Click on add new Plugin
Then search for “EASY THEME AND PLUGIN UPDATE”
THEN ACTIVATE THE SELECTED PLUGIN
As simple as it looks this is all you need to update your plugins and themes manually.
Once this plugin “EASY THEME AND PLUGIN UPDATE” is activated, theme you can upload your new version of your theme or plugins to update the previous version in your wordpress website.