Display fullname order

Troubleshooting
1

I want to change fullname order.
normal: firstname, lastname
want to: lastname, firstname

func (u *User) GetFullName() string {
	if len(u.FirstName) > 0 && len(u.LastName) > 0 {
		return u.FirstName + " " + u.LastName

In this code, I think it cannot be.
I don’t want to build from sources.
Is there any way?