That doesn't remove the job completely.
To remove, double click job to be removed, select history, click on work done, click amend, click reduce or delete the cash recieved, click ok, repeat for each transaction for that job, double click the job again, this time there will be a box that says "delete" click that ....... job done.

I f you do do this it WILL alter all of your figures from the start of the job untill it is deleted, ie, a £10 job done 10 times will reduce your total eanings figures by £100.