Let me share the steps on how you can subscribe to the Spanish version of QuickBooks. At this time, can't directly change your current version to Spanish. You can either cancel or retain your account, then purchase a new QuickBooks with the desire region (Spain or any Spanish country). If you wish to cancel your account, make sure to export your data to Excel before doing the process for future use. For the instructions, check out the details from this link: Export your reports to Excel from QuickBooks Online.
On the other hand, here's how you can purchase a new Spanish version of QuickBooks: