It is possible to redeem banknotes that are no longer valid as legal tender, that is to say, banknotes from older series. The section on "invalid banknotes", which you can find in the menu on the left describes the procedure, how long it takes before you can obtain compensation and the fee the Riksbank charges.
With regard to damaged and discoloured banknotes, they can usually be redeemed at any bank. However, sometimes banknotes have been substantially mutilated or manipulated and this can mean that the banknote/remains of the banknote must be sent to the Riksbank for an assessment and possible redemption. You can read more about this under the sections "damaged banknotes" and "discoloured banknotes". The latter also has pictures of discoloured banknotes.