Next time don't double post, against forum rules. Anyway you'll update to gen a then gen b. So this is how its done firstly download this file here http://www.psp-hacks.com/file/1745 and extract to PSP/GAME/Gen A or what ever you want to call it. Then install the update. After that download this http://www.psp-hacks.com/file/1764 and place at PSP/GAME/Gen B and install from PSP. Then you can delete update files. You should now be at 5.50 gen b. Your Done! Though to be honest I my self would stick to 5.00m33-6 cos my plug-ins don't work on gen b. Still PlayStation store doesn't work so I might update.
Once "B" is on, can we use Network Update for future updateS? Just installed "B" and it says network update has found a later version...
Yes it will update to the latest custom firmware through a network update but it is probably more safe you do it from an update file just in case.