Changing Magento theme could be little tricky with those who’re not familiar with Magento backend. In this tutorial, I will guide you step by step how to change and switch Magento theme in Magento 1 and Magento 2.
Changing theme in Magento 1
First you need to install Magento themes.
After the installation is done, go to Magento backend > System > Design > click on Add Design Change
Next, in General Settings >Â Store, select the store view you want to apply the theme to.
In Custom Design, select the theme you want to change for your store.
Date From/to section let you set the period you  want yo use the theme for, leave blank if you want to use the theme permanently
Everything is done, now your website has been switched to the new theme.
Note: sometimes, the new theme may not be displayed properly in some pages on your site. To fix this, you will need to set proper page layout in CMS > Pages
Changing theme in Magento 2
To change theme for a Magento 2 store, first, go to Admin > Store > Configuration
In configuration, go to Design > Design theme. Here you can select the theme you want to change to.
Next, click on Save config.
Finally, clear cache to apply your change
