There is no upgrade for the MCTS in 2.0 to 4.0 because getting an MCTS on version 4.0 only requires passing one exam (contrary to the MCTS on 2.0 which requiered two exams).
If you want to get the MCTS on Web development on .Net 4.0, you only need to pass exam
70-515. There is no equivalent in version 4.0 to the old exam 70-536 that you needed as a prerequisite on version 2.0.
Edit: If you want to go beyond MCTS and you wish to obtain the MCPD, then you also need three additional exams: 70-513 (WCF), 70-516 (Data) and 70-519 (PRO).