I don’t know of any clients still running Windows XP but there may be some who don’t automatically apply Windows updates when they become available.
If you employ IT support for your site then get in touch with your IT team and check that they have your system supported against wannacry.
If you do not have external IT support, manage things yourself and have not applied security patches recently then I suggest you reconsider and run automatic update and accept any new security patches, if you are not sure how you can learn how to do this here:
Windows 7 users:
Mac users can take the opportunity to feel a little smug but do be aware that its unlikely that the NSA is just looking for Windows exploits, the next NSA leak may be a Mac vulnerability: