I took my car to my local garage when I needed to change to an alko tow ball took them about 5 minutes and no charge and they can do the bolts up to the right torque etc
You said change the 'towbar' but I think you mean the 'towball'. If it is the towball then you just unbolt the 2 x 16mm. nuts and bolts from the existing towball and replace with the Alko towball but make sure you put plain washers under each bolt at the front and spring washers on the nuts at the rear at tighten the two fixings equally.