If all goes well, you just upgrade the JAR's and make sure the databaseSchemaUpgrade property is set to true. If the engine boots for the first time, it'll notice the version of the engine differs from the one in the DB and will do all needed DDL-statements on the db to ensure the correct datamodel is used from that point on. All data will remain in the DB, nothing to worry about.
To be 100% sure, first try it out on a clone of the DB you're about to upgrade and run any product-specific tests (if any). We have upgrade-tests, but could be that there are certain constructs which are a bit different in the 5.14 (eg. customisations), so additional testing is never wasted…
