How to replace Unicode characters with ASCII

Question

I have the following command to replace Unicode characters with ASCII ones.

sed -i 's/Ã/A/g'

The problem is Ã isn't recognized by the sed command in my Unix environment so I'd assume you replace it with its hexadecimal value. What would the syntax look like if I were to use C3 instead?

I'm using this command as a template for other characters i'd like to replace with blank spaces such as:

sed -i 's/©/ /g'