The current situation:
HEAD detached at v3.9.1
* (HEAD detached at v3.9.1)
$version = 2020061501.00; // 20200615 = branching date YYYYMMDD - do not modify!
// RR = release increments - 00 in DEV branches.
// .XX = incremental changes.
$release = '3.9.1 (Build: 20200713)'; // Human-friendly version name
$branch = '39'; // This version's branch.
$maturity = MATURITY_STABLE; // This version's maturity level.
(We have specified the specific current release when installing servers, as we have unfortunately been tickled by issues in the past when the (not actually) "STABLE" version has moved forward to a new updated release between the times when we setup our test and live sites.)
I'm never entirely sure/comfortable about the exact steps needed to tell git to update to a newer version from the upstream repo. What do I need to do to tell it to update our site from v3.9.1 to v3.9.7?