UNIX for Dummies Questions & Answers

Hello all,
This is my first post here, so please excuse me if this question is too obvious or has been asked before. I am new to Unix and although I tried to search your forum for the answer to my question, I could not find an answer that would help me.
I have a 500MB csv file with numeric values as percentages, i.e., 6.56%, or (4.35%). I need to replace the "%" with an empty character, the ")" also with an empty character, and the "(" with a "-" sign. Can someone point me to the right command in unix to do this? Standard Mac text editors blow up because of the size of the file.
Thanks a lot for your help!

Code:

#  echo "6.56%, or (4.35%)." | sed 's/[\%\)]//g;s/(/-/g'
6.56, or -4.35.

HTH