Is it possible to change my user name in win10 in my MS account?

Hi, welcome to tenforums.

From the searchable tutorials section (do feel free to have a look) I found this for you:
Change User Name of Account in Windows 10

Hope it helps.

I don't see a way to avoid that.. clearly others have asked.

Miltiades said:

Hi experts and forum,
I would like to have your advice please:
In all my machines I'm signed in with the same user name: "Miltiades". This has helped me a lot all the last years with sharing in network between the win-pcs.
Noe in the one of them (Win10 pro, 19041, 191206-1406), in which I'm now typing, signed in with my MS account, Windows uses my full name (more than one word), instead of "Miltiades", which I would wish to have also here.
Is this please possible?

This PC where you are signed in with your Microsoft account, have you always used an MS account sign in? Or did you originally use a local account with the user name: "Miltiades" which you later switched to a Microsoft account? It's east to check. If you had set it up as a local account initially then your user folder will be C:\Users\Miltiades. If it was a Microsoft account from the beginning then the user folder name will be the first five characters of your email address.

If it was originally a local account then you can still connect to it from another PC using the "Miltiades" account name. When challenged for credentials you'll need to use your Microsoft account password to connect. That name still exists even thought the account is now a Microsoft account, and the name will return as your account name if you switch your account back to a local account.

Switching from a local account to a Microsoft account, or back to a local account, does not create a new account each time. It is always remains as the same underlying account with the same name for its user folder, just with a different name at the sign in screen and using a different password.

Switch to Microsoft Account in Windows 10
Switch to Local Account in Windows 10

Miltiades said:

Thank You!

- - - Updated - - -

Hi Bree, thank You for Your response.
I can't remember what exactly was with this account, but the user folder has, as you write, the first five characters of my Email. So I think ther is nothing to do about this. Many-many thanks for the effort of You for my issue.
Miltiades

If you like you could add a second account, make it a local account with the name Miltiades. All your other PCs could then access this PC's shares using that account. You don't even need to ever sign in to it, the fact that the account exists is all that the other PCs need to gain access.