I try to send out renewal notices about a month before your service expires. On that email notice there is a PayPal link. This link will take you to PayPal and should have the correct amount set for you.
PayPal is the only way that I can accept payment (except for large blocks of email boxes). You do NOT have to have a PayPal account in order to pay with a credit card. However, you will find it much easier for some locations in the world if you do.
PayPal is safe… as safe as any other payment processor. Because they are more careful at making sure that you are the one that indeed is requesting payment with your confirmed credit card account, I think they are actually preferable, especially since most of our users are situated outside first world countries.