The "update" command:

Usage: fossil update ?OPTIONS? ?VERSION? ?FILES...?

Change the version of the current checkout to VERSION.  Any uncommitted
changes are retained and applied to the new checkout.

The VERSION argument can be a specific version or tag or branch name.
If the VERSION argument is omitted, then the leaf of the subtree
that begins at the current version is used, if there is only a single
leaf.  VERSION can also be "current" to select the leaf of the current
version or "latest" to select the most recent check-in.

If one or more FILES are listed after the VERSION then only the
named files are candidates to be updated.  If FILES is omitted, all
files in the current checkout are subject to be updated.  Using
a directory name for one of the FILES arguments is the same as
using every subdirectory and file beneath that directory.

The -n or --nochange option causes this command to do a "dry run".  It
prints out what would have happened but does not actually make any
changes to the current checkout or the repository.

The -v or --verbose option prints status information about unchanged
files in addition to those file that actually do change.

Options:
  --debug          print debug information on stdout
  --latest         acceptable in place of VERSION, update to latest version
  -n|--nochange    do not perform changes but show what would be done
  -v|--verbose     print status information about all files

See also: revert