what is the best method to keep it and update it there?
Um. Write a schema-builder script. Check it in after making changes. Check it out before running it.
It's hard to determine what you're asking for.
Write formal schema migration scripts. Check them in after testing. Check them out before running them.
What more is there?
What happens is that schema changes turn into gnarly problems because the schema evolves organically through a series of undocumented changes.
This organic evolution makes schema migration more difficult because there's no "authoritative" source for what's supposed to be there. There are two slightly different production versions, a staging version, a QA version and eight development versions. All slightly different.
If there was a single, authoritative source, then schema migration is just the delta between last version and this version.