Hello,
It's unclear if you are talking about the link to bitstreams in the User Interface (which should change to the new URL automatically, once you update "dspace.url" in your dspace.cfg) or metadata fields (which will not change automatically). I'm guessing maybe
you may be talking about updating metadata fields that contain the old URL as their value?
If you are looking to change metadata fields in bulk, the easiest way to do so would be to use the Batch Metadata Editing tools. They will allow you to export the metadata to a spreadsheet (CSV) and then do a bulk find & replace of the old URL to the new one.
https://wiki.duraspace.org/display/DSDOC6x/Batch+Metadata+Editing
If you have further questions, let us know on this list.