The tappets on your car are hydraulic and can't be adjusted.
As for the oil not being changed since you've got the car, do you know when the last owner changed it?
I would change the oil and filter just to see if it makes a difference as the oil you have in there may be old, go to the VW dealer and get a genuine filter and some quantum silver.
Sometimes an oil change will do the job, if its still tappety after this then you are gonna have to replace your bucket tappets and Euro car parts are good for these.
