switching from VARCHAR(255) to a blob

i have a comments thread setup but i initial set the datatype to

if i wanted to allow users to post more than 256 characters...what is
the best way to do this?

should i change the data type to a blob? would this corrupt all current
data in the comments?

Change to it to TEXT and optionally set a maximum size, otherwise the default is 64K I believe (for MySQL that is).

-- gw