That depends. If you have the Climatronic system (seven fan speeds, dual controls for left and right) then you can upgrade the controls to Mk6 or Mk7 easily enough. If you have Climatronic with the "AC" button it's a straight swap - you just need the new controls and the new bezel. If you have the older version with the "ECON" button then some rewiring is required and it may not work quite as well afterwards. You can search this forum for "Climatronic upgrade" for the details.
If you have the manual climate controls (four fan speeds) and want to upgrade to Climatronic, that involves taking the dashboard out and replacing the air conditioning assembly. You can probably find what you need at a breaker's yard fairly cheaply, it's just a question of whether it's worth the effort.