I want to upgrade from self employed to simple start but I dont know how to unsubscribe

You may open your new QBO account with the same email id with current discounted price for up to 6 months. https://quickbooks.grsm.io/US

https://quickbooks.grsm.io/us-promo 

Then cancel your QBSE account with these options:

Purchased directly from QuickBooks or Intuit

1. Open QuickBooks Self-Employed in a web browser on your laptop or desktop. You can't cancel from the QuickBooks mobile app.
2. Select your Business Name next to Settings ⚙. Then select Billing info.
3. Select Cancel your account and follow the onscreen steps.

Purchased from the Apple App Store (iOS)

1. On your iPhone or iPad, open Settings for your device.
2. Select iTunes App Store.
3. Sign in to your apple account. Then select your Apple ID.
4. Select View Apple ID.
5. Under Active, select Manage.
6. Select QuickBooks Self-Employed and then Cancel Subscription.

Purchased from the Google Play Store (Android)

1. On your phone or tablet, open Google Play.
2. Sign in to your Google account.
3. Select the Menu ☰ icon.
4. In the Subscriptions section, look for QuickBooks Self-Employed.
5. Select Cancel and follow the onscreen steps.

Hope it helps