I'm seeing a lot of threads like this on the forum lately, the short answer is Yes, you can change your grades completely without a resit.
However, AS makes up 50% of the whole thing, and because it's normally easier, resitting it would be a good choice if you want a higher grade overall. Getting good AS results is important, even if you resit the exam in Year 13, it's worth it.
BDDU is not a bad set of results, it's not brilliant, but you can get into certain universities if you got BDD again at A2. So you're in Higher Education territory.
If you want to do better, figure out what you did wrong at AS, did you start revision too late (or even too early)? Did you revise effectively? Was your exam technique off? Or was it just bad luck? Have a think, chat with your teacher, work out an action plan and kick ass.
With a bit of revision, self-motivation and commitment you can raise your D up to an A hassle-free.