Hello and Welcome !
Click Start | Right Click on Computer | Manage then Expand Users and Groups and Double Click on the the User name you want to remove and Click on Disable the account. Click ok. This will just disable the account.
If you want to delete the user. Go to Start under search type in Control userpasswords2 there you'll find an option to delete an Account. Create a Restore point before you make any chances.
Hope this helps,
Captain