This could be the information you are searching for, since you land to this page means you are to update your Epic 4G to Android 2.2.1 Froyo. There is a how to guide to update Android 2.2 Froyo for Epic 4G by XDA member Kennethpenn which is explained in detail to help you to do the updates, including the necessary download links.
However installing Android 2.2.1 update DK28 on Epic 4G will make you lose root ability on your Android device, but don't worry you always can to re-root it again, using Z4root one-click app to root Android Froyo.
Before start the Android 2.2.1 update's guide, please re-check whether you have chosen the right packages based on your firmware since there are different packages for both 2.1 and 2.2.
Here is the tutorial link (XDA Developers Forum) to update from Epic 4G to Android 2.2.1 Froyo.