https://www.desidime.com/discussions/how-to-upgrade-from-dcb-to-infinia?page=1#post_9676681
Moving from Diners to Visa in not possible, per HDFC. You should speak to your RM - he/she would help you in surrendering your DCB and then to move to the Infinia in Visa platform.
Source: Personal Experience (Delhi)
And the acceptance of diners is a big problem
In Mumbai, I have not had a problem with DCB acceptance at all at various merchants that I have used it at. The only two issues I have encountered are that DCB attracts a much higher fee on petrol pumps than VISA/Mastercard/RuPay and that Tap2Pay works but with a PIN. For online, I had an issue using DCB a couple of times for some small transactions/merchants.
The regular DCB does an annual fee waiver on spends of Rs 5L or more. DCB Metal and Infinia do that on Rs 8L or more. So that's a plus for regular DCB if your spends are near Rs 5L. Both DCBs also have 2X RPs on weekend dining that Infinia doesn't. Infinia though credits 10k RPs in case you don't meet the spend based criteria and are charged the annual fee. Neither of the DCBs have this provision.
Infinia's SmartBuy RP limit is 15k pm, DCB Metal's is 10k pm and DCB Regular's is 7.5k pm. You would need to book hotels worth Rs 25k or flights worth Rs 56k to to hit the 7.5k pm limit.
I personally wouldn't trade my DCB for an Infinia because it hits a very sweet spot for me.