How add, delete or change field of table?

If i want to do it i can't do it because there are consrains which don't allow me to do it.

It can be done to delete all schema and make it newerely
using scripts, but i am iteresting is there another method to make such operation?

I know that in Oracle 8i i can do it, but does anybody
know how do it on Oracle 7.3.4???

Please, Help

It is a question of all MY LIFE!!!!!