Ps4 – change the PSN name

Yes, since April 10, 2019, you can now change your PSN name.

First, be aware that you can only do so once for free. After that, each change will cost you $5/£4 if you're a PS Plus subscriber or $10/£8 if you're not. You can also call support to change back to any of your previous names for free however.

Changing your name is also only guaranteed to work for games published since April 1, 2018. Most older games, PS3 games, and Vita games will have issues, and you might lose game progress or DLC. Here is a good video going over some of the issues, but to summarize some examples: Little Big Planet and Call of Duty 4: Modern Warfare surprisingly work fine with the new name, Grand Theft Auto 4 and Modern Warfare 2 treat it as a new PSN account, and Black Ops 2 completely fails to load if you're signed in and can irreversibly corrupt your PS3's hard drive if your try signing in with the game running. So, uh, yeah, be careful.

Now on to how to do it, as taken from Sony's help article:

Change Your Online ID from Your PlayStation®4

Step 1: From your PS4 go to [Settings].
Step 2: Select [Account Management] > [Account Information] > [Profile] > [Online ID].
Step 3: Enter your new online ID.
Step 4: Follow the on-screen prompts to complete the change.
Once you complete the change process, you are signed out from all your devices.

Change Your Online ID from a Web Browser

Step 1: Sign in to PlayStation™ Network Account Management and select PSN Profile in the menu.
Step 2: Click Edit button next to your current online ID.
Step 3: Enter your new online ID.
Step 4: Follow the on-screen prompts to complete the change.
Once you complete the change process, you are signed out from all your devices.

Any further questions can probably be answered by Sony's FAQ on the subject.

Unfortunately, this is not possible, at least according to the UK site. (I assume the same is true in Italy; they don't seem to have the same screenshots on the Italian site, though.)

When you create a Sony Entertainment Network account, you set your country of residence - in your case, Italy. This can't be changed later, as indicated in these screenshots. Because the country in the billing address for any forms of PSN payment must match your indicated country of residence, you can't add a credit card from any other country or change the country of an existing credit card.