Only the President has more power in classifying info.
Authority to classify information resides at various levels. People low on the administrative totem pole, including field operatives of all sorts, can classify information they convey if they believe that secrecy is required, but their decisions will be reviewed by specifically responsible officials. The government's highest classification authority is the President. Not only is the President's decision final if there is an interagency dispute about whether information should be classified, but the President can classify or declassify any information regardless of agency objections. On occasion, the intelligence community has shuddered when Presidents revealed sensitive classified information in speeches or conversation. No wrong was committed, however, because no matter what harm disclosing information may cause, the President has the authority to reveal it.
Presidents seldom get involved in the classification process, however. Rather classification authority is delegated down to the federal agencies that deal with security and diplomatically-relevant information. Within each agency, the agency head is the highest classification authority. Thus, if the allegedly classified information in Clinton's e-mails had been labeled Secret or Top Secret by some lower ranking State Department official, there would be no issue beyond one of Clinton's good judgment if she decided to declassify and discuss it. An agency head cannot, however, declassify information first classified by a different agency. Thus according to news reports, the e-mails provided the Justice Department apparently mention only information classified by CIA and NSA.
http://www.brookings.edu/blogs/fixgov/posts/2015/08/13-hillary-clinton-classified-emails-lempert