Hello Cekkasster-gmail, 

Welcome to the  Community page, 

There is no way of upgrading from Self-Employed to Essential. It would be a case of exporting any information you would like to keep from your self-employed account and saving it to your pc then canceling your account and taking out a new account in QuickBooks on the essentials package. 

@cekkasster-gmail 

You may need another reference

https://quickbooks.intuit.com/learn-support/en-uk/other-questions/how-do-i-export-all-my-data-from-m...

If you have to open a new QBO account, make sure to click the Buy button to get the discounted price for up to 3 or 6 months. If you purchase from the Trial account, you have to pay the regular rate.

https://quickbooks.grsm.io/UK