It means you used a table name that doesn't exist in the database, or a column name that doesn't exist in the table. In your case it's the latter. If you had printed out your SQL you might have noticed that right away: it would look something like
update customers set firstName = Moose where customerId = 5
And the name you put in there -- Moose in my example -- is not the name of a column in the table.
In SQL you have to put 'apostrophes' around string literals, so one correction would be to add those apostrophes to your string. But a better correction would be to use a PreparedStatement, which lets you use parameters. Like this:
That takes care of the apostrophes for you, and also deals with problem cases like where FirstNameText contains apostrophes itself. And when you decide that customerId needs to be a parameter too, replace your "5" by a question mark and call