T2's usually make plenty of their own insulin but have become resistant to it.
Insulins job is to take the sugar out of our blood and deliver it to our cells & muscles to be used as energy. Our bodies can't use our insulin efficiently so our blood sugar levels remain high. Carbohydrates when digested turn to glucose and will cause high blood sugar levels. So reducing the amount of carbs in your diet should improve your levels.
The Glimepiride you are taking works by encouraging your pancreas to produce extra insulin, changes to your diet needs to be done along with careful monitoring of your blood sugar levels. It's possible that a lower carb diet together with the Glimepiride could cause your levels to go too low, in which case your medication will need adjusting.