Hi mate,
Its fairlty straigt forward. Undo the two 10mm bolts on the battery retaining strap. Disconnect the negative terminal, and then the positive. Then lift the old battery out. The clock will die straight away..so you will have to set the time again. You've got ages before the ECU resets (hour or more) so plenty of time to get the new battery in. The positive first, and then negative...put the retaining strap and two bolts back on and your done.
Hope that helps,
Alan