Changing username

Not sure if this is correct place to ask but even though my email is linked to.my ps account etc, the first time I logged in on here, I never got asked for one, and instead just have loads of random letters / numbers. Is there a way to change it? I’ve had a look at profile etc but can only see a way to change personal details. Know it’s not F1 related but I will be on here a lot so felt like best place to ask. 

thabks 🙂