Here is a tutorial on how to change the front and rear differential fluid in your BMW E90/E91/E92/E93 (xDrive). Probably very similar for 335 and M3 models. Quite the messy job so have some towels ready. The front and rear diffs take just a tad bit more than 1 quart of fluid (Redline 75w90 was used) so make sure to purchase at least 3 bottles. You will be filling these until fluid starts dripping out.

Make sure to remove your fill plug BEFORE your remove the drain. That way if for some reason the fill plug is stuck on, you can still use your vehicle. since the fluid hasn't been drained yet.

Here are a few amazon affiliate links to some fluid pumps (As an Amazon Associate, I earn from qualifying purchases):

Soap dispenser style:
https://amzn.to/3LJy4hw
https://amzn.to/3PXWoii

Larger extractor hand pump:
https://amzn.to/3LIX88q
https://amzn.to/3PW2zmV
https://amzn.to/3RIBV23

Brake Bleeder Pump (used on the rear since it uses a smaller tube):
https://amzn.to/3LKuQdJ

Fluid Used:
Redline 75W90 GL5 (both front and rear) https://amzn.to/3rJo15c

Torque Specs:
Drain/fill plugs 44 ft/lbs
Skid Plate/cover bolts 41 ft/lbs plus a 90 degree turn (I prefer goodandtight for these though)