Thankyou all for your replies. woofgang ,two roots of my orchid have come up through the compost ,thats why I was thinking of repotting it .Its the third orchid that I have bought the other two died ,this one seems very healthy ,apart from the roots coming up ,and I dont want to lose it .I must admit ,I thing I gave the other two ,too much water .
They like to be kept on the dry side. Also keep a look out for mealy bugs - mine got infected this year, and I was advised to re-pot and use new compost, also wash the roots. I found the blessed things were even clinging to the little clips that hold the flower up straight!
They like the light, but not strong sunlight or else the leaves can burn.