How to change how many posts show on the homepage (Hueman)

Hi there. On my homepage, I currently have the featured image slideshow, and then underneath that there are 21 posts listed (in two columns, with images and a short extract for each) before the ‘Next page’ link at the bottom.

I am wondering if there is a way to have, say, 10 or 12 posts listed instead? An even number if possible would be great, I think.

I looked around the customiser but probably missed where the controls are for this. Thanks for your help!