Repotting and the roots on top of soil?

[plumeriastix]

Well this makes post number three and I'm sure it's one of my dumber questions to date, I know there's not supposed to be any dumb questions but I have them, believe me

All three of the orchids I just bought have roots all over the top of the soil. They are all in 6" plastic pots and still seem to be happy after 48 hours with a notorious orchid murderer

I am wondering if these should be repotted after they finish blooming and if the roots on top should be buried below the soil line in a new pot or left on top of the soil (orchid mix)? Also, if I do need to repot would I go up to a 7" or 8" pot? Two of the three plants are dendrobium nobiles and the third is a cym.

Thank you all for your help. I have read a lot of threads but a lot of what I am reading is greek to me, you guys have your own wonderful orchid language and although I am trying to learn it I need a botanical dictionary beside me which I don't happen to have

for any help you can give to this newbie

Best wishes,
Jerri