Can't re-install OSX

When I purcahsed this Macbook it was running Snow Leopard then upgraded to Lion and now Mavericks.

Lately I am having problem updating Apps from Itunes, it shows a different Apple ID and I can't change it.

I have tried all and various ways to solve that problem but to no avail. So I decided to re-install OSX using the original DVD provided.

It shows you can't run this version. So I tried using the Disk Utilities but prompted Apple ID and Password.

Frustrastingly, it mentioned this wasn't the password during the purchase of the Maverick. I have all ways but gave up.

Please assist, thanks.