Ok, you need to measure the frame size of your current glasses so that you can find a suitable pair to fit your face well. However, you don’t have to worry too much since the exchange/return policy has become very friendly nowadays for online shopping.
I am a regular customer who shops online a lot. Let me check, you should start with a prescription paper, frame measurements, a credit or debit card for the payment. Uh, a deliverable address for sure. You should be fine with them.