Hello Arunasala,
Follow the steps given below to change/create the slider.
Step 1. Go to Dashboard >> Slider
Step 2. Click on Add New button
Step 3. Add the slider name.
Step 4. Add the slider content.
Step 5. Add slider button link.
Step 6. Add slider button text.
Step 7. Add the featured image as a slider.
Step 8. Click on ‘update’ button at top right of page.

You can use the “1400*675 px” size image for slider.

Here is our theme step by step complete documentation link given below, you may follow it to set up your site as our demo.
https://luzukdemo.com/demo/digital-marketing/documentation/
Thank you.