Yes, but not easily. There’s no direct way to transfer between the two competing payment services. You can withdraw to your bank and then deposit to the other platform and vice versa. This could take a few days to complete, though.
Alternatively, you can use a third-party transfer service to add this capability directly on. We wouldn’t recommend it, though, as it adds an extra player into the mix and the whole idea behind e-wallets like Neteller is their simplicity and speed.