Hi Ayushi Sharma,
Welcome to CodeRanch!
Apart from cost, if I had to give those exams, I would've chosen either OCPJP 6, or OCAJP + OCPJP instead of OCPJP 6 + OCPJP 7 upgrade.
The reason being, upgrade exam only gives emphasis on what's new in
Java 7 (or at least what's new in OCPJP 7 - e.g.
JDBC is not new to Java, but Oracle has added it to OCPJP 7). But with OCAJP 7 + OCPJP 7 you get one seperate exam just for basics (OCAJP) and another exam for little (ok, not little) advanced topics - and the exam is in general for Java, instead of some specific version of Java.
Btw, have you already completed
SCJP 6? In that case, personally, I don't see much value in going for OCPJP 7. I myself have cleared SCJP 6 and I'm not going for any Java SE 7 certification.
If you haven't completed SCJP/OCPJP for Java SE 6, then I would suggest you can think of that also. It'll cost even less money (because in any case you'll have to give only one certification) and since differences between SE 6 and 7 are not astronomically large (like they were during 4 and 5), OCPJP 6 is not 'outdated'.
I hope this helps.
All the best.