The 757 v4.x is no longer available to purchase, so I'm assuming you bought the 757 Captain III Base Pack.

Anyway, here's how you can download them:

Login to Your Profile > Select product (757 Captain III (757-2PW) Base Pack [P3D4/5] (or [FSX/SE/P3D3]) > Extended Download Service > Click on the server link to download

If you need to create an account, make sure you use the email address that you bought the broduct with so you will see the product(s) you purchased.

Note. I purchasedd several items yesterday, and the email with the links didn't show up for a couple of hours (even though it shows it was sent at the same time as the reciept email with the link to the forum). I had already downloaded and installed them using the above method by the time I recieved the download links email.
By the time you read this, you may have recieved the email with the link(s) to the download. Also. check you Junk email for the email from Captain Sim with the link(s)