You will need to log into cPanel with your supplied username and password. Normally this URL is: http://www.yourdomain.com/cpanel
1) Select the Username field and enter your username
2) Next select the Password field and enter your password
3) Now select the Log in button
4) From the Files section, click on the File Manager icon
5) When prompted select to open the Web Root and click the Go button
6) Select the directory named 'joomla' by clicking on it
7) Next right click the folder name and select the Rename option
8) Add the letters 'my' to the directory name and click the Rename File button
9) Now double click the 'myjoomla' folder
10) Select the 'configuration.php' file and right click. Then select the Edit option
11) Select the Edit button
Scroll down to the bottom of the editor window
12) Select the place in the $log_path where we will edit it to match our new directory name
13) Change the path to read 'myjoomla' from just 'joomla'
14) Do the same for the $tmp_path value
15) Next click the Save Changes button
16) Now select the Close button
17) Select Yes to close the window
You now know how to rename your Joomla directory from cPanel