nuby : adding new fields to existing table

I am starting rails with the clean slate(no legacy tables).I created
tables and fields in sqlite using a gui.I am more comfortable this way.I
did rake db:migrate. this updated the scheme.rb .After which I created
Model .This basically has the same set of field as in scheme.rb for the
But now when I want new field to the table in sqlite how should go about
telling rails to update the scheme.rb and 001_create_table.rb file .Or
should I do it manually.
what is the normal way of doing this migration.Should I start from rails
and it will create the table for me ....

When you run "rake db:migrate", your schema.rb will get updated, and it
will run any migrations that haven't been run.