Don't take this the wrong way, but if you have to ask what a low pressure oil pump is, and where it's located, let alone how to change one out, I think you are better off paying someone to do it for you, if it is indeed the cause of your issue.
Now comes the million dollar question. WHY is it not building low pressure oil?
If I were you, the first step is to remove the oil pressure regulator to see if it's stuck open. If that fails to reveal anything obvious, the next step is to pull the gear cover off for closer inspection.
This being on an E-Series makes the job that much more horrible.
Sidenote: Low Pressure Oil Pumps seldomly fail, unless it has ingested some foreign debris.