image sizes and ppi?

My uploaded pics into theme are too small and not correctly sized. Within your theme instructions you have published: Image Sizes Feature Post Slider Width: 1140px Height: 450px Thumbnail in Homepage and Archive Page Width: 690px Height: 462px Small Thumbnail Width: 390px Height: 261px My question is how many Pixels per inch (ppi) should I set my Adobe Elements setting to correctly size my immages?