Drop down menu hidden behind slider

Hi,

I am hoping that someone will be able to help me!

I am relatively new at WordPress and still very much learning. I have built this website, and for some reason drop down menu that shows when you hover over is hidden by the slider.

The slider is a SiteOrigin slider. The drop down menu (services) is showing fully on all the other pages, including the About page which shows the menu on top of an image.

I have read a few forums on here that mention the probable issue is the Z-index, however whilst I think I understand what this is, I have no idea how to find it to make amendments!?

Can someone please help me?

The website is http://www.metatrainfitness.com

Any help would be appreciated!

Thank you in advance
Gareth