Changing a Child's Name: I Wish to Change My Name (Age 17)

My question involves name change laws in the province of: Ontario

I have come to the decision that I want a legal name change.
This is a very big deal to me and a hard decision. I have many reasons and just want to be free and untagged. I am not bored with my name, I quite like it, but this is my only way to feel comfortable and just be happy.
Ive thought long and hard about it and I really do wish to change it, I want to change my first name to something new and use my middle name as my last name.
I'm just really afraid of my mothers reaction when I tell her.. I would completely understand if she was aposed to this; she carried me, birthed, named and raised me... she ought to wonder why I want to change the name she chose for me. I do have reasons, many and I feel so deeply. I only dream of the day that I can walk up to someone, they do not recognise me, and ask my name.. and I can be freed of my burdens and comfortable with the real me!
We already have a very rough relationship and I'm afraid it will become worse. I am 17.
I have lived on my own for a year until I recently moved back in with her.
She has a mental illness and constant mood swings, so I dont know what a good time would be to bring it up, maybe dinner?
My father passed away so I dont want to get rid of my last name, i just wouldnt want to disclose it to people, because the whole point of changing my first name is to start fresh (im not a criminal or anything) Ive just been through a lot, and have lived a lot for my age. I wish to just rid of all negativity and just be the real me, not have whats tagged with my old name dragged everywhere I go.

So, I wish to break to my mom that I want my first name changed, and figure out a way for people to not know me or my last name.
any help? If anyone understands me?
thanks.

also how do I go about doing this legally, what must I do?