I ordered EX280V45K but I'm not sure whether it means EX280 with OCP v4.5.
If so, the OCP v4.5 is no more officialy supported and should I contact someone from Red Hat to upgrade it accordingly to a newer version?
Appreciate your advice. Thank you!
Yes, EX280V45K is based on OpenShift 4.5.
And EX280V46K, which is based on OpenShift 4.6, is already available.
If you want to take the EX280V46K exam instead of already purchased EX280V45K, I would suggest contacting Red Hat training people.
However, I think there shouldn't be big changes in the exam, because there is no meaningful difference between the TOCs of DO280(OCP4.5) and DO280(OCP4.6).
 You can find a list of contacts at https://www.redhat.com/en/services/training-and-certification/contact-us#tab.contact-method.1