Forum:Understanding Upgrades - HELP!

I'm playing ME 1 and I am having a horrible time understanding how the upgrades work.

For example: I have four  First Aid IV upgrades in my inventory. Do I need one for each character, or just one total for everyone?

Also, how do you properly install/uninstall upgrades on XBOX 360. The game doesn't seem to allow me to remove them singly. How do you tell? If I tell it to uninstall, it doesn't appear to happen.

How do I tell a weapon which ammo to use? (Xbox 360)

Any help would be appreciated.

Whe wiki does a great job of explaining what ammo does what, but I can't find a guide that explains the mechanics.

Example: To install the "upgrade"  do A, B then C.  To remove one "upgrade" do D, E and F.  Sell X upgrade when you get Y upgrade because you don't need X  any longer.....that kind of stuff.