You can try this
Create a small ftp server, create a share folder “/routeros/6.28/” depending on the versions you what to upgrade. Extract all the package to the folder “D:/routeros/6.28/”
On the RB that you want to upgrade do the following:
/ip dns static
add address= “Your ftp server ip” name=upgrade.mikrotik.com
/system package update
check-for-updates
:delay 1s;
:if ( [get current-version] != [get latest-version]) do={ /system package update upgrade };
Reboot RB.