Which history are you referring to ?

Look in advanced Privacy options, this will delete the logs.
Although not permanent as files on your machine are never really gone "forever".

Tools > Options > Privacy > Privacy Settings > Advanced options > Keep history change to NO history, also click Clear history.

How to change your Skype account "User Name" - Skype Community (http://forum.skype.com/index.php?showtopic=216951)

If you are referring to your username, which you use to login, you can not; you will have to open a new account and use a different login name. If you are referring to your display name, you will open your skype, go to tools, go to options, look under general, click on general settings, look toward the bottom right in blue where it says Add contact details to your profile, change any info that others can see (including your display name) and then click on update.

I was referring to my username! Anyway , thank you for your answer!

Changing Your Skype User Name
Log in to your Skype account.

Click the "Skype" tab, and select "Profile" and then "Edit your Profile" from the toolbar at the top.

Edit or change your name in the "Full name" box.

Select "Update."

Log out and log back in to Skype.


Hope this helps you :)

To clear chat history in Skype...
Login to your account.
Go to Tools>>Options>>Privacy>>Privacy Settings>>Show advanced options
Now click on the Clear history, now you will not be able to see history anymore.

OR

To disable chat history,
Login to your account.
Go to Tools>>Options>>Privacy>>Privacy Settings>>Show advanced options
Look for "Keep History for, and select no history. You can also select for 2 weeks, one month and forever.


Hope this helps you :)

Are you referring to the sign-in field PRIOR to signing in? Is it pre-filled with your username? If that's the case then that is typically remembered by your browser through the "Auto-Complete" feature. You need to clear your auto-complete history which will clear all auto-complete histories. In IE, click "Tools", "Internet Options", "Content" Tab, under "AutoComplete" click "Settings", then click "Delete AutoComplete History...". This will clear the entire history. There might be a way to clear just one entry (I haven't looked for it) and there are similar ways to do this in other browsers as well.

Hope this helps.

Thank you very much to everyone!