A Will can be cancelled simply by creating a new Will which states that all previous Wills are revoked. Your current Will will be automatically revoked if you marry or enter into a Civil Partnership. A clause may be added to stipulate that your current Will is not to be revoked by your intention to marry or enter into a civil partnership with the named partner.
Alternatively, a Will can be revoked by destruction, for example, by burning, tearing or otherwise.