Hi Reshma Shanbhag,
It will be helpful to know how to prepare for the exam and what are the reference materials.
The details about exam like exam cost , number of questions, time, format, syllabus,etc is here
OCPJP8Upgrade. The exam objectives contains mainly Java SE 7, 8 versions added features. If you already have basic knowledge about those concepts, You can follow two books such as
Oracle Certified Associate Java SE 8 Programmer I by Sybex, Oracle Certified Associate Java SE 8 Programmer II by Sybex. If you don't know first get some basic knowledge about the concept and then go through the above two books.
I can suggest you the book Java The Complete Reference by Oracle Press to get basic knowledge about the concepts.