Change the length of days your customers have before their Shopping Cart purchased downloads expire.
To do this follow the steps below:
1. Under 'Commerce' choose 'Shopping Cart'
2. Choose 'Edit Shopping Cart Settings' from the shopping cart menu
3. Look for the field 'Download Days' and change the amount of days you wish your customers to have to download their product before the download link expires.
Enter 0 (zero) to allow the purchaser to have an unlimited amount of time to download the file.