c:\boot.ini

it's hidden, system, readonly.
Use command ATTRIB -R -S -H c:\boot.ini, then you can read it.
After change, make sure do ATTRIB +R +S +H c:\boot.ini to prvent delete it accidently.

Using explorer, you can try folder options, show hidden, system files. Then you can use property to modify the attribute.

Unless you know what you are doing, you should change through Control Panel, System, Startup(???).