Usually if you are carefull not to move the dish it’s a straight forward swap. Sometimes because of the extra weight of the lnb and cabling the dish may need a tiny nudge up or down. (depends on whether the lnb arm or the mount flexes more – if you are lucky they will both move very slightly and compensate for each other). You can’t get twin lnb’s for Sky Minidishes so it will have to be a quad.

NeilC – 51 minutes ago  » 

Thanks Graham – do you have a recommendation for the best Quad LNB?

Assuming you live in the UK pretty well any will do. Fleabay is likely cheapest, The lnb fittings vary with the age of the dish so unless yours is a new Mk4, buy one that comes with the legacy adaptors.