need help in php file upload

I Am trying to create an simple image sharing website, i need a help with the file upload script. when a user uploads a file it should be renamed and stored in the server just like tinypic.

here is my php code:

Now what is the code snippet and where should i add that in this script to rename the uploaded files?

please help me Thanks in advance..

 

Just edit the line that says:
"upload/" . $_FILES["file"]["name"]);
to
"upload/imgnamehere");