Been taking 1/4 klonopin (clonazepam) m&n and 10mg of celexa m. After 2 days I started 5mg of celex & felt depressed. Can I go back to the 10mg, is it safe?

Yes, it safe. I would also add that Klonopin (clonazepam) can cause depression. It is used for concomitant anxiety in depression but not used solely for depression. Depending on your age and weight, the 10 mg. of Celexa maybe too little.
Not a DIY project. Dosage of psychotropic medications is very tricky even for experienced professionals and the impact on your body of switching around can be big. Don't do it w/out a doctors guidance and monitoring - up or down. Call for an appointment ASAP. If it was only one day on the half dose, I expect you could go back up and think of it as a missed pill, but please learn not to make changes on your own.