How can you shrink hemorrhoids?

Depends. Minor hemorrhoids can be "shrunk" with proper diet and fluids, avoiding caffeine excess, and correcting diarrhea or constipation issues.
Soak. Sitz baths (soaking in warm water) and ice can both help shrink hemorrhoids temporarily. Avoid pushing or straining when you have a bowel movement. Increase fiber and fluid intake. Don't use a donut pillow - this can actually aggravate hemorrhoids. Wipe gently and avoid irritating the hemorrhoids. Wipes can be irritating. An oily cleanser like balneol can be helpful. See doctor if no improvement.