Incorrect name is showing as "sender" on emails.

My computer seller set up my Windows Live so I could send emails with cut and paste photo option.  This works fine, but now all my mail goes out

with someone elses name on the message.  It shows the sender as as a person from my contact list.....not me!  How do I change the sender name?

When someone receives an email from me.....it displays this other person....not me.  Therefore, they are deleting messages.  If I send emails through

Internet Explorer, all is okay.  It only happens when I send or forward through Windows Live.

Please help and thanks,  Cheryl