I still managed to upgrade all instances with SP3.

I use SQLServer2014SP3-KB4022619-x64-ENU.exe

from https://www.microsoft.com/en-us/download/details.aspx?id=57474

Thanks everyone for your help

It is really an Express version.

SELECT SERVERPROPERTY('Edition') AS [Edition]    result in

Edition

Express Edition (64-bit)

A separate install for each instance?

The installation on instance SQLSEXPRESS succeed and result in version   12.0.6024.0.

An later...

The instance name SQLEXPRESS is indeed not meaningful.

The supplier of the Mamut package installed this system and chose the instance names.

In the beginning of the installation of the SP3 upgrade,...

I execute the upgrade to SP3 with SQLEXPRWT_x64_ENO.exe (1.143698Kb)

on the database server MAMUT-SERVER\SQLEXPRESS

The upgrade was performed with no error messages.

When I login to MAMUT-SERVER\SQLEXPRESS and I execute SELECT @@VERSION I...

De SQL Server Management Studio is 32 bit but the SQL Server is 64 bit.

I will try again with SQLEXPR_x64_ENU.exe

New problem.

See attachment.

As you see SQLEXPR_x86_ENU.exe (size 286.128 kB) give not:

"Upgrade from SQL Server 2014" (without SP3) to SQL Server 2014 (with SP3)

The Windows...

The result of the query SELECT @@VERSION is:  "Microsoft SQL Server 2014 -  12.0.2269.0 (X64)"

I don't understand that (X64) because this query is executed in:

C:\Program Files (x86)\Microsoft SQL Server\120\Tools\Binn\ManagementStudio\Ssms.exe

This give "Upgrade from SQL Server 2005, SQL Server 2008, SQL Server 2008 R2 or SQL Server 2012"

But I don't see "Upgrade from SQL Server 2014".       (without SP3)

Can this Upgrade...

That is a link to SQL Server 2012 SP3 Express.

I need a link to  SQL Server 2014 SP3 Express.