Making “Posts Longer”?

Hello ?? I had a question about my WordPress. On my site, my sidebar is longer (like it stretches the page) more than there are my WP posts. I was wondering if there’s an option to change for how many posts show on your site. Like I have 10+ pages of posts but how can I change from 7 posts show to say, 10? Is that possible? Let me know if I have to explain more. Thank-you!