Hi, dependes on wich theme, the speed can be changed in custom.js . Tell us wich theme are you using.
As i said before, you didn't pay for this HelloSlide extension, it's free. You paid for the theme, wich yes, it has a "Completely customizable frontpage gallery slider on frontpage to showcase latest products or special offers...", the .js files control the slider, mostly custom.js
What is broken is the extension HelloSlide, not the theme. Since the extension is free, we will fix it when we have the time to do it.
Tell us the theme you are using, so we can tell you what you have to change in .js files.-