how to upload apple mail emails to hotmail

i recently set up my hotmail on the apple mail program for my macbook air.  i didn't realize that it defaulted to POP email set up.  anyways, all the emails were downloaded onto the macbook air and deleted from the server.  this causes a problem since i access my emails from multiple computers and mobile devices.  so my question is, how do i get the emails that are sitting on my macbook air transferred to the hotmail server?