For your protection, and in order to release the prize money to the contest winner, both of you must legally transfer ownership of the design. Therefore, sending of design files should be done ONLY through the site and NOT through email or other offsite means.
Freelancers will be able to send you the files for their design through the site. This feature has been made available to users because sharing contact information like email addresses or phone numbers is not allowed.
Each designer/freelancer who enters your contest will be able to submit several entries if they wish. The maximum file size per entry is 250 MB. When you select a winner, both of you will have to complete the Handover process.
Transferring files is done through the Contest Handover page because, in the process, you would both have to sign an IP Transfer Agreement, which transfers the ownership of the design to you. The winner will then upload and submit the design file on the same page. The maximum size one can upload on the Contest Handover page is 200 MB per file.
Once you review the submitted files and you are absolutely happy with what you've got, you can go ahead and accept them. The winner will get the prize and you will then have complete ownership of the files.