Deeper theme customization (beyond theme options) can be done in CSS. If you are familiar with it, you can use FireBug (FireFox plugin for web-developers) or Chrome web developers tools to determine which CSS rule should be changed and where it is located. Here’s a helpful screencast on how to use it: https://www.youtube.com/watch?v=nV9PLPFTnkE
Dynamic styles are stored in the theme folder > “css/custom.less”. LESS CSS user guide can be found here: https://lesscss.org
Recently we started providing paid customization services. So you can take advantage of using our Custom Shop services: https://custom.dream-theme.com
You can also consider hiring a freelancer to help you: https://www.upwork.com/, https://studio.envato.com/