A few weeks ago, I saw a thread about bashing wiper arms with a hammer to remove from the spindle, when they're seized on. This is how i got mine off.
1. With the bonnet up, lever the caps off and remove the retaining nuts with socket. Spray with WD40
2. Whilst WD40 soaks in, unpack the new kit, inspect, assemble blades to arms.
3. After about three minutes, with the bonnet down, remove the old wiper blades from the arms. This enables you to work on the wiper arm with the bonnet up again
4. With the bonnet up , pull the arm back on the spring, & turn against the spindle. No need to give a sharp tug, just firm presuure, gradually increasing until the "seal" between trhe arm and the spindle breaks. Once it does, the arm comes straight off.
5. Position the new arms and blades nice and low on the spinbdles, screw the retaining nuts on & refit the caps.