You can either send a cheque (or cash?) to their postal address:
Karmel St. Joseph,
Korbacher Str 89,
59929 Brilon Wald,
Germany
...or you can make a bank transfer to the following account:
Sparkasse HSL Brilon, BLZ 416 517 70, Account No. 56 267
For an amount of any real size between countries you might need the BIC and IBAN codes.
IBAN: DE58 4165 1770 0000 0562 67
BIC: WELADED1HSL
Which method works out as better value for what size being transferred, I don't know. For a small amount it might be better to just put a cheque in the post. But then of course they'll have to pay currency exchange.
You might also want to ask someone in your bank, to be sure.