Hi Robina,
You have many options available to you (including the schools listed on this site). While they will all cost money, there is a vast difference in that cost (so, if that is important, look carefully at each listing).
Now, the following advice is for most students who want to get a high school diploma from the U.S. while living abroad:
1. Make sure that the school is accredited by a regional or national accreditor listed at
http://www.chea.org. If you are not sure, come back here and ask. You do not want to earn a high school diploma at a school that is not acceptable to anyone.
2. Choose a program that allows you to submit assignments via email or a website drop box system. You do not want one that requires you to either mail or fax assignments. The first is abysmally slow and the second can get quite expensive.
3. Choose a program that will allow you to transfer in all previous high school credit. You absolutely only want to finish the diploma and not to work on things that you have already done.
4. Let them know that you are presently living in Pakistan (or, for other readers, whichever country you live in). Most online high schools are quite familiar with international students and their requirements. Do not choose a school that views that as a problem.
Do you have additional questions? If you give me more information about your situation (like ability to pay or length of time to be in Pakistan, etc.), I may be able to offer more suggestions.
Tom Nixon