Editing mistakes in recording income

Hi, I've just entered my income for April - the first time I'm using this system. After completing that task I realised that I'd made errors on most of the income figures as it's joint income so I meant to log only 50%. I now can't see how I can edit these figures. Is it possible to edit income figures once saved? Or will I have to void or somehow delete everything that I've done an redo? Hope not! Thanks.