It is possible within your Storefront to edit the name displayed to a customer of the Payment system you are offering them in the checkout.
For the example above, you may want to change "Purchase Order" to "PO Number" or "Credit/Debit Card" to just "Online payment" or even specific to Paypal if that is what one of your payment options is.
These labels are controlled using our language strings.
So to find out information on how to use and where to update language strings read our article on it here
When searching for the specific language resource depends on the payment plugin you have enabled on your storefront.
The format for the Resource Name should be as follows:
For example, To rename SagePay, you would filter by a Resource Name of 'Payments.SagePayServer.FriendlyName'
The value you enter here is what the customer will see on check out for that specific payment plugin.
Repeat this step for all of you payment plugins you want to amend the labels for.
Don't forget to save all your changes.