Updating SilverStripe databases is pretty easy, because you just update the code and run dev/build?flush and you’re done. Unfortunately between SS 2.3 and SS2.4 the character encoding changed and when you have a lot of broken Umlauts after updating.
If you ever have to update a really old site you can manually convert the database dump using iconv in your shell:
iconv --from-code UTF-8 --to-code ms-ansi -c dump.sql > dump-with-umlauts-fixed.sql
Then you can import the converted dump and update your site.