need help with 121w

[kamak]

As I have read on internet I need to change my LNB to linear. Is anyone can say how i can visually differentiate linear LNB(11700-12200) and circular LNB(12200-12700) Also, I don’t know what size of the dish should be for 121. I have 20 inch dish which I pick up 110. Is it ok? Or I need 30 inch dish also. I know that there is difference between 110 & 121 but I don’t know much about it so please explain me how I should tune up to 121. Thanks in advance.