If the workorders are checkmarked Service Completed, but not yet checkmarked Closed, than you can un-checkmark the Service Completed (which exits the workorder, than you open it again) and than you can make the changes you need.
Workorders that are checkmarked Closed can not be edited or deleted, as they have been closed. Closed workorders are for historical viewing only.
There is no need to delete “old” workorders. Doing so would mean that you would lose historical information. If you do want to delete old workroders and the workorders are not checkmarked Closed, to delete you open each workorder and select the Delete menu option.
By default grids display the first 100 records that meet the filter gridsettings - for example, if you have the Service Date column listed as the first column in the Service Workorders grid in AyaNova v3, select the sort image on that column to sort the records with the latest workorder record listed first.
I encourage you to refer to the AyaNova v3 Manual section “Use Basics” starting page 26 which goes over the different ways of filtering, sorting, pinning and viewing the grids so that you are displaying the records you want to view.