Old transactions in Purchase & Sales registers

Hi, I need to tidy up a MYOB Accountright plus file that has transactions in the Sales register dating back to 2015 and back to 2014 in the Purchase register.  The Accountant has asked me to tidy up the file of all the old transactions that have most likely been paid, via spend money, but not marked off the purchase register.   Can someone help with the best way to do this?  We report our BAS on a Cash basis.