I have a database setup with utf8mb4 but the old tables and columns are still utf8_unicode_ci. What's the easiest way to convert them all to utf8mb4_unicode_ci? I tried to use this method but got the following error:

ERROR 1071 (42000) at line 15: Specified key was too long; max key length is 1000 bytes

The only other way I can find is: https://mathiasbynens.be/notes/mysql-utf8mb4 but I have far too many tables to go through one by one.