Ibrahim’s comment on the other answer is the correct way to alter an existing user’s home directory.
Change the user’s home directory:
usermod -d /newhome/username username
usermod is the command to edit an existing user.
-d (abbreviation for --home) will change the user’s home directory.
Change the user’s home directory + Move the contents of the user’s current directory:
usermod -m -d /newhome/username username
-m (abbreviation for --move-home) will move the content from the user’s current directory to the new directory.