Ucommerce includes full API reference documentation and lots of helpful articles to help you build your e-commerce site as effortlessly as possible.
Upgrading Ucommerce is done with the Ucommerce installer in versions newer than 7.0.
When upgrading use the same install options as when you are doing a first time installation. Ucommerce automatically upgrades all files and migrates all database tables, when an existing version is detected. Afterwards the back-office and API's are running in the new version.
All that left to do is test the frontend for breaking changes.