1) start: miktex -> maintenance -> package manager(admin) //you need to be admin to install this
2) Then you need to update the data base of the package manager:
in the package manager: Repository -> synchronise
3) with in the package manager GUI install the necessary packages, in this case:
- l3kernel
- l3packages
- siunitx
4) In order to apply the changes you need to refresh the local data base
start: miktex -> maintenance -> settings (admin)
click on: - refresh FNDB
- update format