There are two main methods to install a WordPress theme.
1. You could use the integrated theme search engine.
Go to Appearance->Themes->Add New. Now choose from the presented options.
2. You could upload a theme you’ve downloaded or purchased from a third party theme provider.
Go to Appearance->Themes->Add New->Upload Theme.
3. Choose the theme file, located on your computer.
Method 1 : Install WordPress theme from WordPress.Org
This step is the common ground between the two main methods. You have to enter the theme options. Now, you’ll be able to see all the themes that have already been installed.
Click on the Add New button above the other themes.
You will be given a list of themes.
Find a theme that you like->Hover over it->Click Install->Click Activate.
Method 2 : Upload theme from your Computer
STEP 1: Enter the Theme Options
Let’s say you’ve bought a theme, or downloaded one from a third party theme provider. To upload it to your site, you have to go to Themes. Then click Add New. Now click the upload Theme button.
STEP 2: Upload the Chosen Theme
A menu will show up. Click the Choose File button, select the archive of your theme from your computer and press the Install Now button. WordPress will finish the operation automatically for you. Just click Activate afterward.
