Blog summary or full text

Hi! On my blog page the posts are represented by a small summary each containing around 20 words. How do I make the excerpt longer? I want to show perhaps 100 words before the "Read more" link or maybe even the full post. I've tried Settings->Reading->"For each article in a feed, show" and set that to "full text" but nothing changes. Is there another way to do it? Also (less important), when I choose a page to be the posts page (in WP settings->Reading) that page loses it's title and sub-title for some reason, showing instead the name of the website and the website tagline as a sub-title. Can I do anything about that? My solution right now is to set one page as the default posts page (with the wrong title) but to link to another page that also holds the posts and that has the title I want it to have. Thank you.