If you already have an ongoing premium "one instrument" yearly subscription and would like to upgrade to the "all instruments" plan click the 'upgrade' button below your Yousician level and profile picture in the top left corner of any tab:
Alternative way is to switch to another instrument and follow the standard upgrade procedure - you will see all options available for your profile.
Choose the available option and proceed to the payment.
When upgrading from a yearly "one instrument" plan it will look like:
When upgrading from a monthly "one instrument" plan it will look like:
Read this article about upgrading Monthly "one instrument" to Yearly "one instrument" (same instrument) subscription OR Monthly "one instrument" to Yearly "all instruments" subscription.