As SiC you should have rights to change your own position.
First, make sure that there is at least one other player who is a CiC or SiC. Promote them if you have to.
If the other player is inactive or not cooperating, then boot them from the alliance.
As long as someone else can be left in command, you can demote yourself.
It sometimes takes more than one step.
Demote yourself to Officer first, then if you can't leave the alliance, demote yourself again.
If you can boot all other players from the alliance, then you - as the only one left - can disband the allaince from the main alliance screen. ( description screen)
I'm just another player.. if you need help from someone at EA, then go to the help center at Help Center link
