Once in Builder, you will see the operations list, locate the operation in this list that you wish to update the attachment on. You can use the Filter to find an operation if you know the name, opcode or source opcode of the operation you wish to update.
Click on the operation name.
You can delete an existing Uploaded File by clicking on the trashcan icon. If you want to add another file and keep the existing one bypass this step.
Click the BROWSE DOCUMENT button.
Select the document you want to upload and click Open.
Enter a Document title.
Then click the UPLOAD button.