Exam 70-551 or 70-553

I'm an MCAD and also MCSD
I want to do the exam :- UPGRADE: MCAD Skills to MCPD Web Developer by
Using the Microsoft .NET Framework
If i do exam 70-551 what will i have to do to get MCPD?
And again whats the difference between 70-551 and 70-553?
Having both MCAN and MCSD which will be the best one to do..
Thanks alot
Patrick

Patrick.O.Ige