Same here @sverre.klein11 - no prompt to set unique username.
I have another account with a company email address which is onboarded as Partner. In that case I was promted to set unique username.
But not here as “ordinary” member. 
Perhaps here lies the cause?
Hi @sylwia.ganie my username here is @paul.merin which is truncated and would like to set it correctly.
Is there a way to do this?
Thank you have a great day!

I couldn’t change my user name either.  I signed in with my email. 

• Then found a place to edit my profile, but there was no place to edit my user name (nothing that I could see)…..

Hi,

Thanks for reporting this. There is no option currently on the platform where you can change your username.

I am investigating, 1) why you have not been asked to set your username with the first access , 2) how you can set a username of your choice. 

I will come with a response soon.