Where can I find replays in-game?
Click Single Player in the main menu and choose Load Game. The Saved Games tab will show saved single player game modes, including standard and campaign games. The Replays tab will show recorded single and multiplayer games
Replays from previous updates
A replay file from a previous update will no longer be playable and will include the message "This replay file was created with a different build of the game than the one currently used. Attempting to open it may result in premature end of playback." If Yes is selected, then often the replay will open but will end very quickly. There is not a way to restore replays from previous updates.