I believe member titles are automated, and they depend on how many posts you have- you changed from member to veteran member because you reached a new plateau of posts (300, in your case) Here is the list of titles, and the post numbers that reflect them:

• Newly Joined - 0
• New Member - 1 post
• Junior Member - 6 posts
• Member - 20
• Veteran Member - 300
• Grand Member - 500
• Poohbah - 1000
• Grand Poohbah - 1500
• Magnate - 2000
• Grand Magnate - 3000
• Elder - 5000
• Wise Elder - 7500
• Legendary - 10000
• Legendary Wise Elder - 20000
• Wisest Elder Ever - 50000