Hi Lawrence,
You need to download support patches from service.sap.com/swdc > Support Packages and Patches
> SAP ERP > Entry by component > SAP ECC Server. Select Component you want to update. It will give you list of patches. ABAP patches are not cumulative and you need to download (003 to 0023 for appl in your case ) all components and extract all components and put all .pat , .att files in sap eps/in folder and run spam as suggested by MJ.
For smooth upgrade make a list of dependencies. Click on Info beside component list, it will give you Package Import Conditions in new window and check all Import Conditions are met.
Instead generate support stack file from solution manager and download components.
Regards
Mahesh Kumar