Hi how do i change my email address on this account. Thanks

You can add the multi user app by going to Cog->Manage Users – add your email account as a new administrator for your company – then logout. An email invite to Bullet will be sent to your new email account. Click the link and login in with your new credentials.
You can go back to “Manage Users” and then disable your old email address’s access to the company. You can then cancel your trial for multi users from the app store.