The only alternative is to wait. In the future, make sure you read the "Salesforce Sandbox Preview Instructions" for a particular release (which is emailed to administrators in advance). Some sandboxes must be refreshed during the preview window to get the next release, and other sandboxes must not be refreshed during the preview window to get the next release. If you don't pay attention to these schedules, then you'll have to deal with having the wrong version until the final upgrade schedule. Support may be able to fix this for you, but there's definitely no way you can fix it yourself if you don't pay attention to the opt-in/opt-out periods.