Hi and welcome,
FIRST OF ALL BACK U ALL THE DATA YOU WANT FROM THE CURRENT HOME DIRECTORY
To change the name of the home directory you will need to go to System preferences found on the dropdown menu under the black apple on the tool bar. Click on "Accounts" you will now have to unlock this by clicking the padlock icon and entering your password, then click the + icon to add a new user Fill in the details you want ie the name you want the home directory to be. Click on " allow user to administer this computer". close system preferences and log out of your computer then login using the account you have just created. Once you are satisfied you have all the data from the old account you can then go to system preferences and delete the account you no ln longer want.
I hope this is of some use to you