Your database really shouldn't be that large for 500 posts.
I have a few thousand posts and my database is around 8 MB.
First, before we try anything, make a backup:
https://codex.wordpress.org/WordPress_Backups
Next, I suspect that post revisions may be taking up the majority of the space (which is usually the case, especially if you edit posts/pages frequently), so if you have access to phpMyAdmin or the MySQL command line, enter the following query to remove all of your revisions:
DELETE FROM wp_posts WHERE post_type = "revision"
(Note: you'll need to replace wp_posts with the name of your Posts table)
Let us know if that made a sizable dent.