I am using toshiba tecra a4. Can somebody tell how to lift the keyboard so that i can change it.

The following link will give you an idea of the fun involved in removing your keyboard. (hope this helps)

http://tech.irisvista.com/laptops/Toshiba4010/portege4010_1.htm

(Steps 5-7 are probably the most helpful)

Generically speaking, you usually take the keyboard off by removing the top panel that is above the keyboard. With a screw on the side, or on the bottom, under this panel. Once the panel is off, it reveals a few screws for the keyboard which is easy to spot.

On more rare occasions, there can be an extra screw on the bottom that goes into the keyboard.
But normally, some type of panel has to come off and kb will have a screw or two under the panel.

Good luck!