You want to issue the chown (change owner) command, for example:
chown user /home/user
The command above will change just the folder /home/user. If you wanted to change all of the files and folders within a given directory you would use:
chown -R user /home/user
If you wanted to change the user and group at the same time you would use:
chown user:group /home/user
Where ‘/home/user’ is the path to the directory. If you wanted to change one file then you would specify the file at the end of the path. Please be VERY careful doing this.