inside stair safety codes

I want to look into making my stairs less steep and pretty much remaking them. These lead to the basement, so doing this would give slightly less head room, but think I can manage to do it without it being too much of an issue.

I know there are certain code requirements such as the minimal head room, the size of lumber to use for the framing, how much of the wood must remain after making the triangle cuts etc...

Could someone tell me what are code/safety things I need to keep in mind while doing this job? Guessing this varies per region, I'm in Ontario, Canada.