don't remove it:
The Update Cache folder for Microsoft SQL Server is found in the
C:\Program Files\Microsoft SQL Server\\Setup Bootstrap\Update
This article provides information to help you understand why this
folder is created and what it's used for. More Information
When is this folder created and what is it used for?
When you install any SQL Server update (cumulative update, critical
update, or service pack), the update installation media is cached in
the SQL Server Update Cache folder. The entries in Add/Remove Programs
are created from the contents of the cached media folder and are used
to uninstall (as necessary) the most recent update that was applied to
a particular component. The folder may contain multiple earlier
updates, allowing for sequential removal of those updates if required.
A variation of this model occurs when a component was installed by a
stand-alone MSI file instead of by SQL Server Setup. These components
are serviced in-place by replacing the previous MSI file with the new
one, without maintaining a history of previous versions. The original
MSI file is required for both uninstall and repair operations.
When is this folder cleaned up or removed?
When all patches are removed from all instances, or when the product
Why does the folder continue to grow in size?
The folder grows in size with each update that's applied to your SQL
Server instance. This growth occurs because each earlier version must
be cached. This behavior ensures that you can always access an earlier
update if you need to.
What happens if you remove this folder or delete its contents?
If the Update Cache folder or some patches are removed from this
folder, you can no longer uninstall an update to your SQL Server
instance and then revert to an earlier update build. In that
situation, Add/Remove Programs entries point to non-existing binaries,
and therefore the uninstall process does not work. Therefore,
Microsoft strongly encourages you to keep the folder and its contents