A memorial is a message to somebody. In our diocese, messages and memorials have been sent mainly to General Synod, although they could be sent to other bishops, other synods, the Council of General Synod or elsewhere. A memorial is a useful way to talk about a matter that is ultra vires, or beyond the powers of Synod.
As members of the national church we have no ability to change doctrine or worship, except as delegated by General Synod (Article II of the Constitution). However, we may send an unsolicited message to General Synod (which does have authority over such things), provided that the memorial has the support of two-thirds of both laity and clergy at Synod.
To learn how to draft and submit a memorial see "How to Make a Motion" in the Synod Manual.