If I upgrade to QB Plus and can then use classes is there anyway of bulk updating previous transactions to include a class. Thanks

Hi usersuzanneflux, thanks for posting on the Community

It isn't possible to batch-update classes in QuickBooks Online Plus. The transactions would need to be edited individually to assign a class. 

There is a reclassify transactions feature which would allow you to move multiple transactions under one class at once, however, this is limited to QuickBooks Online Advanced and Accountant (if you have an accountant added to your QuickBooks, they'd be able to do this for you).