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Database Migration Option (DMO) of SUM - Introduction
The guides are available here https://websmp206.sap-ag.de/guidefinder
https://websmp206.sap-ag.de/~sapidb/012002523100016383942015E/DMO_SP14_Guides.htm
If the system is non unicode then you need to do unicode conversion to bring the system to EHP8
If there are other systems in landscape that are connected to this system then you might need to upgrade them as well. 2200904 - Adjusted Version Interoperability for Business Suite 7i2016