By A Web Design
To install a new template in Joomla core, login to Joomla website as administrator, by simply entering the url_of_your_website/administrator in your Browser. Enter the appropriate username and password {which was provided while installing Joomla } and then click on Login as shown in Diagram 1.

Diagram 1
After logging in as Joomla Admin, a Control Panel page opens as shown in Diagram 2.
The Control Panel provides access to different Joomla functions and features.

Diagram 2
In the top menu, locate Extensions. Click on Extensions, from the drop down menu that appears click on Install/Uninstall as shown in Diagram 3.

Diagram 3
An Extension Manager page opens. In the Upload Package File section, click the Browse button as shown in Diagram 4.

Diagram 4
After clicking on the Browse Button a file navigator window opens. Navigate to the appropriate folder where the Joomla template file is, select and open the Joomla Template zip file as shown in Diagram 5.

Diagram 5
The zip file name appears in the Package File text box. Click Upload File & Install in order to upload the Joomla template zip file and install it into the Joomla framework as shown in Diagram 6.

Diagram 6
Once the template zip file has been uploaded you will see the successful installation message as shown in Diagram 7.

Diagram 7
In the top menu, locate the link Extensions. Click on Extensions, from the drop down menu that appears click on Template Manager as shown in Diagram 8.

Diagram 8
A list of templates in Template Manager is displayed. The template which is active has a yellow color star icon under the Default column, in front of the template name as shown in Diagram 9.
You can verify and preview the new template installed for Joomla core as shown in Diagram 9.

Diagram 9
To make the template currently installed the default template, select the radio-button adjacent to new template name and then click the Default icon at the top-right hand corner as shown in Diagram 10.

Diagram 10
The new template will get assigned as Default template as shown in Diagram 11.

Diagram 11
The template is now installed, activated and set as default as shown in Diagram 12.
To view the installed template in Joomla core, enter the url_of_your_website in your Browser and hit GO.
The Joomla website opens with the installed template as shown in Diagram 12.

Diagram 12
The template is activated and installed for your Joomla CMS is finally completed.
To uninstall template from your Joomla CMS, make another Joomla template the default template as shown in Diagram 13. NOTE: The default template cannot be uninstalled.

Diagram 13
In the top menu, locate Extensions. Click on Extensions, from the drop down menu that appears click on Install/Uninstall as shown in Diagram 14.

Diagram 14
An Extension Manager page opens. Click on Templates as shown in Diagram 15.

Diagram 15
The Templates Extension Manager page opens as shown in Diagram 16.
Select the check-box adjacent to new Joomla template and then click the Uninstall icon at the top-right hand corner as shown in Diagram 16. This will successfully uninstall the plugin.

Diagram 16
After the uninstallation is complete the Uninstall Template Success message is displayed as shown in Diagram 17.

Diagram 17