An NSIS installer is available (/S for silent) but an MSI is also available.   7-Zip will upgrade any older version found, so no uninstall of the old version is necessary.

Install is straight-forward:

7z1900-x64.msi /qb-! /L*v C:\My\Log\file.log ALLUSERS=1 REBOOT=ReallySuppress

(for 32-bit: 7z1900.msi, but 64-bit should be used on 64-bit computers, per the 7-Zip support page)

Uninstall:

64: msiexec.exe /x 7z1900-x64.msi /qb-! /L*v C:\My\Log\file.log ALLUSERS=1 REBOOT=ReallySuppress

32: msiexec.exe /x 7z1900.msi /qb-! /L*v C:\My\Log\file.log ALLUSERS=1 REBOOT=ReallySuppress