jmb7, go to https://ftp.mozilla.org/pub/firefox/releases/115.17.0esr/win32/ and select your language, in there select the .exe file to download. Double-click the downloaded file to install it, that's all.
My W7-Pro/SP1 64-bit on a Lenovo T440p has not had any updates since 2018. I saved the User-profiles for both Local and Roaming before I applied the .exe. Did not deed them in the end, everything A-OK.
As a matter of fact I installed the update without any problems, following the ftp link that I gave above: https://ftp.mozilla.org/pub/firefox/releases/115.17.0esr/win64/en-US/Firefox%20Setup%20115.17.0esr.exe
