Nothing ties you, neither ethically nor legally, to publish your new work (your database update) in the same journal as earlier work on the topic. However, if the journal was a good venue for this particular publication some years ago, the same reasons probably still hold, which means it's still a good place to publish your update. If, however, you feel like changing, just go for it!
Regarding authorship, this should be discussed right now. If you have full charge of the database, did important work on it yourself, and write the paper, then you have strong arguments to be first author. On the other hand, if you're the new admin but contributed little to the recent improvements, your position is weaker. In the end, it will be the result of a negotiation.