Step 1: Access to your cpanel (www.yourdomainname.com/cpanel)
Step 2: Click on File Manager
Step 3: Click on public_html
Step 4: Click on wp_content
Step 5: Click on themes
Step 6: Click on Upload
Step 7: Upload your theme in zip format
Step 8: After you uploaded the theme, click on "go back to"
Step 9: Right click on the theme.zip format and click on "Extract"
Step 10: Click on extract file
Step 11: Go to your WordPress dashboard >> Appearance Themes >> Activate the theme you uploaded