Follow these steps to upload your theme in VirtueMart:

STEP 1: Log in to the Control Panel.

STEP 2: From the top navigation bar of the panel, navigate to Extensions -> Manage > Install.

STEP 3: Click on the browse button and install the theme by clicking upload and install button.

STEP 4: After uploading the theme, you can set the theme as your default theme.

STEP 5: Now you may visit the site and can see how it looks on the browser.