This is how i did mine if i remember correctly.
First check too see if you can get the fill bung undone.
Remove drain plug and remove oil and then pump, 2 x 10mm bolts, clean filter, I took mine off but be super careful as the filters aren't available separately.
Replace o rings on the pump if you want, I didn't nor did Paul70 iirc, there about £20 from VW.
Clean round where the pump fits in the diff housing.
Smear a bit off diff oil on the o rings and fit the pump back.
Refit drain plug and fill until oil drips out of fill plug, nip up plug, then run the pump relearn with VCDS, run up for a couple of mins, temp of diff oil has to reach a specific temp I can't remember off hand, before checking.
Remove fill plug and top up if needed just until oil just seeps out..
Stand back, light your pipe and admire your handywork.
If the pump filter is clean a relearn is not strictly necessary, but if its dirty and made up I would do a relearn.
The pump measures the current required needed to reach max pressure and this will be much more if the pump is blocked.