My users with new Membership receive Mail with Sender "Wordpress", can I change this ?

I type this as general Topic cause I think that´s not only a problem of Membership2 Pro that I installed short time ago.
My users receive Email with sender "Wordpress" and a text like "Wellcome to membership ABC..." or something similar.
I use WP_Symposium Pro and there are Mails sent with sender "Amsyri.net" as my website is called and I wanted to have this on my WP-Mails too.
Can you tell me please where I can change this ?
Thanks, Richard