How to increase column size in Redshift database tables?
In AWS Redshift is now possible to alter ONLY VARCHAR column but under these conditions:


You can’t alter a column with compression encodings BYTEDICT, RUNLENGTH, TEXT255, or TEXT32K.
You can't decrease the size less than maximum size of existing data.
You can't alter columns with default values.
You can't alter columns with UNIQUE, PRIMARY KEY, or FOREIGN KEY.
You can't alter columns inside a multi-statement block (BEGIN...END).


See the documentation.