Use chown to change ownership and chmod to change rights.
use the -R option to apply the rights for all files inside of a directory too.
Note that both these commands just work for directories too. The -R option makes them also change the permissions for all files and directories inside of the directory.
For example
sudo chown -R username:group directory
will change ownership (both user and group) of all files and directories inside of directory and directory itself.
sudo chown username:group directory
will only change the permission of the folder directory but will leave the files and folders inside the directory alone.
you need to use sudo to change the ownership from root to yourself.
Edit:
Note that if you use chown user: file (Note the left-out group), it will use the default group for that user.
Also You can change the group ownership of a file or directory with the command:
chgrp group_name file/directory_name
You must be a member of the group to which you are changing ownership to.
You can find group of file as follows
# ls -l file
-rw-r--r-- 1 root family 0 2012-05-22 20:03 file
# chown sujit:friends file
User 500 is just a normal user. Typically user 500 was the first user on the system, recent changes (to /etc/login.defs) has altered the minimum user id to 1000 in many distributions, so typically 1000 is now the first (non root) user.
What you may be seeing is a system which has been upgraded from the old state to the new state and still has some processes knocking about on uid 500. You can likely change it by first checking if your distro should indeed now use 1000, and if so alter the login.defs file yourself, the renumber the user account in /etc/passwd and chown/chgrp all their files, usually in /home/, then reboot.
But in answer to your question, no, you should not really be worried about this in all likelihood. It'll be showing as "500" instead of a username because o user in /etc/passwd has a uid set of 500, that's all.
Also you can show your current numbers using id i'm willing to bet it comes back as 1000 for you.