Amit,
By default, the Enter key is mapped to the StartEditing action (in the WhenFocused input map) and StopEditing action (in the WhenAncestorOfFocused input map). You can remap the Enter key to the MoveToNextRow action using the following code...
fpSpread1.GetInputMap(InputMapMode.WhenFocused).Put(new Keystroke(Keys.Enter, Keys.None), SpreadActions.MoveToNextRow);
fpSpread1.GetInputMap(InputMapMode.WhenAncestorOfFocused).Put(new Keystroke(Keys.Enter, Keys.None), SpreadActions.MoveToNextRow);