How to turn off all constraints in a table?

[Tomáš Vichta]

Hello,
I need to turn off all constraints in a table (especially primary and 
foreign keys) - because for example I need to exchange primary key 
values of two rows in a table. And because of primary key constraints I 
can do it directly. I would to turn off the constraint, rename value of 
PK1 to PK2 - now I have the same 2 values PK2 and it's the problem, if 
the primary key constraint is enabled.

Thanx very much for answer, TV.