The easiest way is to search for the games save folders location (google for it) and save those folders on HDD or USB.
Theoretically, you can't transfer a game from an OS to another. You'll have to reinstall the games and then copy the "save" folders to the same locations.
You really can't because of each games registry entries. In theory you might be able but in the end it is just easier to re-install all the games. With Steam and Origin this can be daunting but really you should re-install.