Upgrading from merchant beta to RC?

[robfico]

What is the recommended way to upgrade a Magento 2 Merchant Beta (master branch) store to the latest Magento 2 RC version? Docs suggest a few ways, but am unsure what the best way is to proceed. Thanks.

[Dmitry_Fedyuk]

I do upgrding the following way:

1. Backup files and database
2. git pull
3. composer update --prefer-source
4. bin/magento setup:upgrade

[robfico]

Unfortunately, that did not work. Previous version was Magento 2 Merchant Beta (master branch) with sample data installed. I had to remove composer.json and composer.json.lock to satisfy git pull (maybe there's a better way?). When running setup:upgrade, this error occurs:

PHP Fatal error:  Cannot instantiate interface Magento\Store\Api\StoreRepositoryInterface

Is there an established path to go from Merchant Beta to RC with sample data installed?