A . If You updated from Typesetter 5.04 or earlier (?) : Typesetter 5.1 is not really php7.4-ready .
( If You have clicked at the update-button in the old typesetter version : It has a different function.)
:: To update to the CE-Version You must replace the /include-directory of the old installation with the /include-directory of the CE-version (make a backup before or rename it).
C. Please use filezilla-portable for the upload because several users had problems with other ftp-clients.
The update to TP5.2 is more complicated, because You also have to replace the gpconfig.php .
P.S. After successful update You should also (only) update the /addons- and the /themes - directories!
Be careful not to overwrite templates which You use and in which You made specific code-adaptions.