To manually upgrade your machine when a new version is released: The build-identifier is normally identified on the release notes of the release you are upgrading to.
As of release 11.2.0, olpc-update only keeps 1 software version available by default (i.e.
the old version is deleted after booting into the new version for the first time).
10.1.3 to 11.2.0), you will probably need more than 300mb of disk space available (even though the upgrade process will finish with approximately the same amount of disk space available).
See the Releases page for the releases that are available.
olpc-update is a command-line program to update your system software.