CODES P0420 and P0500

[gabosan20]

Hi Guys I need some help , I have an OBD scan and I get this 3 codes
P0420
P0420 (the scanner shows some simbol or arrow here I don´t remember wich one)
P0500

Can you tell me what to do first to try to trobleshoot this codes?
Can I take the two O2 sensors and cleaned or they need to be replaced firts they are expensive and no mentione the catalitic converter.

For the P0500 I check and is related to VSS , any help how to cleaned, I could not find the VSS in the van, also I could not find the part on the internet, my speedometer works fine , and the transmission too, any advise.

I try to clear the 3 codes with the scanner but they don´t clear, the firts codes that appear in the van were the two P0420 and I clear with the tool and they came up after a while , now I have the 3 codes adding the PO500.

Please help I need to pass emissions, and try not to spend a lot of money.