Modify database table in runtime

I want to modify a database table in runtime. One of the things I want
to do is changing the size of a text column, maybe also the name, but
this can be solved by using some sort of translation between the real,
and the wanted new name.

I know that in SQL(at least in Oracle) you may do something like this:
        alter table mytable modify (myColumn char(20));
I tried this in Interbase, but it could not understand the modify
word. Isn't this standard SQL? Can I alter a table in another way,
than building a SQL statement on my own, like using TTable?

Thank you in advance for any viewpoints about this.

Alf Inge Lindtner