Customizable is now the standard of WordPress market. So any theme you get from Sneeit.com must have that feature.
For live preview customization, you need to login into your WordPress website dashboard and choose Appearance > Customize and then change any settings you want.
If your purchased theme supports Theme Options, you can access Appearance > Theme Options and change settings from there. The theme option is more convenience than the customizer when you can search controls and settings without need to know where is their location.