Make my icloud email address my primary mail address
I need to change my primary email address from my previous telco service provider to my icloud email address, as the previous telco provider cannot supply landline/broadband facilities to the new area I have recently moved to. At the moment, whenever I send an email, the default email address is my old one, and I have to remember to change it before I send the message. How do I do this please? My iMac is currently running Mojave 10.14.3. I also have an iPad and iPhone; all 3 are synchronised.
iMac 21.5", macOS 10.14