Are you worried about the name changes in your Passport? Then this post is for you!
First of all dont be panic.
Usually our passport will be having three columns.
1. First Name
2. Middle Name
3. Last Name
Do you know, in US the last name is more important than your first name. The University records, SSN, Driving license etc will be addressed with your last name. In that case your last name is very important in Passport.

If your passport received from the Authority ,doesn't contain the Lastname or blank or an incorrect one, then immediately inform the same to the Passport Authority. Make sure your last name changed before you take any step forward like registering for GRE ,TOEFL etc.

I have already registered to GRE with a wrong Last Name??
You already registered with a wrong Last name. Now you are worried on how to proceed. In this case, I recommend you to cancel your schedule and make sure your last name got corrected in the Passport. Go and reschedule for the test with your correct last name and First name.
At this point, you may think that you are losing so many bucks. But it will save you from so many other troubles which will come in future.

Related posts:
Looking to know about the New GRE Revised test in detail?
http://graduateroom.blogspot.com/2011/07/new-revised-gre-test.html

Free GRE and TOEFL score reporting:
http://graduateroom.blogspot.com/2011/10/free-gre-and-toefl-score-reporting.html

New GRE Revised test survery and Analysis by KAPLAN:
http://graduateroom.blogspot.com/2011/08/detailed-analysis-of-new-revised-gre.html

New GRE score reporting schedule:
http://graduateroom.blogspot.com/2011_10_01_archive.html

Documents required to apply for USA Universities:

http://graduateroom.blogspot.com/p/study-in-usa.html

New GRE Books Review:
http://graduateroom.blogspot.com/p/books.html