updating sql

In Oracle 7.3.4, how do I update the number field(10,2) to a negative value?

Its been so long sine I looked at 7.3.4. Why can't you just update table1 set num1=num1*-1 where num1>0; or something like that. Then you can start reading the "10g before you install guide" and start considering how you are going to migrate to 10gR2. :)

Thanks for you reply. I will test it out.
My company is very happy with 7.3.4 and do not plan to move to any other version for some more time or until everything crashes.