Delete those pre-upgrade version files, if possible. (xp_SLS.dll and SLSSqlMaint.exe are located in the <SQLServerInstall_Directory>/MSSQL/Binn directory.)
Though likely you will not be able to delete those files because they are likely currently in use by the SQL Server. In which case you will need to restart the SQL server service in order to release the process to release that file(s) before you will be able to delete those prior version LiteSpeed files.
Sometimes a reboot of the SQL Server machine is necessary to have LiteSpeed see the SQL Server instance, even if you were able to delete the pre-upgrade version files from the SQL Server Binn directory.
Run though the LiteSpeed upgrade again (disable all jobs and maintenance plans that are scheduled to run during the time of the upgrade).
Run extended stored procedure EXEC xp_sqllitespeed_version in the SSMS to confirm that all LiteSpeed software components are now all on the version to which you have just upgraded.