You'll need to download the latest version of system software (OS/Firmware) from the new cart's website as it will be different from the old one.
The old card was probably an original R4 (or clone) that did not support microSDHC (cards over 2GB) and the new 'R4 v3' (one of the many fake R4 carts that support microSDHC) is actually a somewhat different cart.
The different hardware needs different system software.
To my knowledge the official R4 team never released a microSDHC compatible cart before they were shut down.
There should be a URL on the packaging of the new cart.
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