How to change slider images

Hi, I have been battling for hours to try and change the slider images. I don't have the theme options tab on my toolbar. Where would I then change it? I have seen if I add a featured image to the page it shows that image if I select slider image. But it only allows one featured image so I have no idea how to add more images to the slider. I don't have the option of adding any IDs anywhere. All I have is: Appearance = customize = featured slider options then under that there are two subcategories: Featured slider settings and featured slider type. And under neither of them there is an option to add more images. Please help.