I would like to know how to retrieve deleted browser history and incognito data.?

I would like to know how to retrieve deleted browsing history and incognito browsing history. Also, if a website appears in the Adobe flash settings but it's not in the browsing data, I see the name of the site but without the cookies, how can I see exactly what someone was viewing on that site. I'm not up to anything bad, I just have someone using my computer and I believe they are looking at things they shouldn't. I can see from the flash player settings tab that they have been to sites they shouldn't have I delete the history when I'm done so I know what's mine and what's not, but I'm not sure what they were looking at. How can I catch them red handed?