How can I change my 5 month old's middle name in Canada?

[ForestofDreams]

The father and I couldn't decide what to name our son (we had two names we couldn't decide upon) so we used the preferred name as his first name, and the other name as his middle name. Over the time I found that middle name really has no meaning other then being the name we couldn't decide on. I want to give him the name of my father who passed away as his middle name instead. It would just be more meaningful to me and to him too, I believe, plus it sounds really cool in his name.

 

I'm not sure how it works in Canada. I looked online but didn't really find anything involving this precisely. Any help would be great!

[Seraphim]

This is for adults but I am sure you need to contact Service Ontario. link removed. I believe there is a fee of a about $150.