How can I install a template in SMF?
Template installation in Simple Machines Forum.
The most popular way to customize your SMF website is to install a new template.
First you should download the desired template from the Simplemachines.org website, here:
http://custom.simplemachines.org/themes/
After that has been done, log into your SMF admin dashboard and navigate to Admin > Configuration > Themes and layout from the popup submenu.
At the bottom of the “Manage and Install” page you will find the “Install a New Theme” section ( please refer to the following figure).

In this section, you should click on the Browse button and select the downloaded template from your local machine. Once you select your template, click on the Install button to begin the installation.
After installing, you will be displayed with an installation success message.
Now, you may want to activate the newly installed template. Please navigate to Admin > Configuration > Themes and layout and choose the desired template from the drop-down menu for “Overall forum default” (for your convenience refer to the following figure).

Click on the Save button and your new SMF template should be activated successfully.
Please note that its a good practice to backup your website’s content files and its database before changing the appearance of your SMF application.