The scale you are describing is the Melodic Minor Scale. In the ascending form of a melodic minor scale, the 6th and 7th scale degrees are raised (compared to the natural minor scale), while in the descending form, the scale reverts to the natural minor, meaning the 6th and 7th scale degrees are lowered.
For example, in the A melodic minor scale:
- Ascending: A, B, C, D, E, F♯, G♯
- Descending: A, G, F, E, D, C, B
So the ascending form has the raised 6th (F♯) and 7th (G♯), and the descending form has lower 6th (F) and 7th (G).