5a- installs SM 4.1, this downgrades 4.2 and 4.3. It is optional. 4.2 is good, but only supports BB2, where 4.1 supports BB1 and BB2, and 4.3 has killed BB.
5b- updates ios, since your on 4.2 your ios should be fine.
5c- patches a few game ios, you should do this part
When you install the ios, install from NUSD, apply all three patches and your done.
I will update 5a to make it more clear.