If anyone still needs to know how this is done, you will have to modify the donate_plugin.php file which can be found in wp-content/plugins/recurring-donation.
Edit the file and go to line 164 of your php file. If you are using notepad to view this go to the <!– Donate Amount –> comment.
Look for <label for=”first_button”> $ <- this is what you need to modify in order to display your currency. I’m not sure how it works for other currencies, but for £ you will have to use £ to output £ on your web page.
You will also need to modify line 175 and use the correct currency code for paypal to pick this up. In this case I am using GBP so the line will look like this: <input type=”hidden” name=”currency_code” value=”GBP”>.
Same rule applies for line 192 in your code.
<input type=”hidden” name=”currency_code” value=”GBP”>
Hope this helps.