If you have a big database (many post with many photos), i recommend you should to backup data before to do.

How to update a theme:

1 – Go to Plugins –> Add new –> Search for “Easy Theme and Plugin Upgrades

upgrade

2– Click install Now

upgrade2

3- Click Activate Plugin.

upgrade3

4– After installed plugin, navigate to Appearance > Themes. Click the “Add New” button at the top of the page.

upgrade4

5– Click the “Upload Theme” button at the top of the page.

upgrade5

Click the file browse button to select your theme zip file. The button’s text varies by browser. It typically says “Browse…“, “Choose File“, or “Choose…”.

All done!