Cats will not tack from a reach at all. First rule of a good tack is you must be sailing close hauled with the main tight.
As Mary said steer up with steadily increasing pressure on the helm.
As the boat goes through the eye of the wind, ease the mainsheet a foot or so until she is on the new heading, then switch sides and sheet in.
If the sea is flat, you need not let out too much mainsheet when easing, but in heavy winds and seas more sheet may have to be eased.
Rick