make sure to read the "UNICODE Conversion Guide" you find in the SAPNet (Path: SAP NetWeaver -> SAP NetWeaver in Detail -> Application Platform -> ABAP Technology -> Internationalization -> Unicode Conversion Guides).
There you will also find appropriate Checklists.
Check out if you have a single Code Page system or e.g. a MDMP system (using multiple codepages). MDMP system conversion to Unicode is much more complicated. You may have to build up a vocabulary for your texts in different languages / codepages that are stored in tables without language key column (SPRAS).