Definitely possible to do this, but it's hard to say how without knowing which slider your theme is using. There should be some controls for your slider within your script.js or theme.js file. If you're lucky there will be a setting called autoplay that's switched to false. Switch that to true and you'd be good to go.
If you can't find that then you might have to check out the developer website for the slider and check their api. If you reply with the theme you're using I can help you further with this.