It's not under Accessibility, like you'd expect it to be, if we were talking about Windows, or any other OS. It's tucked under 'Device Options' —> 'Display Settings'.
Layout size is barely larger, and only effects a select few things. You'd really expect more on this front. Some UI fonts are very small on Scribe. It's a fairly large device, and can be used at greater distance from the eyes. I find current page and progress percentage fonts just right, but I really wouldn't mind options to have them larger, and smaller. Though, by Amazon standards, they'll increase all system fonts by 200% with no option to reverse that in the next update.