Changing a PSN account on PS3

I just bought a used Playstation 3. I am going to change the PSN account (create a new one) but I have a few questions before doing so.

My brother already started playing a game and he does not want to lose his save file. Can it be preserved? If so how?
If the original owner had bought some DLC from his account and I do not delete the account (keep both accounts on the machine) can I use that dlc? I mean can I install it from his account and use them from my account?
Also the original account was a US PSN account, I am going to create a UK PSN account. Does any of the answers change given that fact?

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Quick Answer about "Changing a PSN account on PS3"

Go to Settings > Users and Accounts > Account > Profile > Online ID.

Create your new online ID.

Follow the on-screen instructions to complete the change.

After you complete the change process, you're signed out of all devices.

How do I unlink PSN account from PS3?

Select your local user account and go to PlayStation Network > Sign-in > Account Management. Go to System Activation and highlight PS3. Select the type of content you want to deactivate for your PlayStation\xae3 console: Game or Video. Select Deactivate System.

How do I create a new PSN account on my PS3 if I already have one?

Press and hold the PS button to reveal the quick menu.

Select Power > Switch User > New User > Create a User.

Follow the on-screen prompts to create the account for PlayStation Network.

Enter the necessary information.

Verify your email address. Check your email for a verification message.

How do I change my PSN email on PS3?

Go to Settings > Users and Accounts > Account.

Select Sign-in ID (email address). Enter your new email address and click Save. You may need to re-enter your password.

You'll receive an email to your new email address asking you to verify your new sign-in ID. Click the Verify Now button in this email.

How to deactivate a PSN account on your PS3 system (psn game sharing)

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