Default time from 12 hour clock to 24 hour clock

Dear All,

I need urgent help please!

I’m as normal user of office 2007. I need to know how can to convert time automatically from 24 hour clock to 12 hour clock. (e.g. 15:47 to 03:47, for more example:
- From 16:33 to 04:33
- From 13:10 to 01:10
- From 19:20 to 07:20
- From 14:00 to 02:00
- From 20:00 to 08:00

Could please help me urgently.

Thank you

Mostafa Saqallah

Thank you very much for your quick help.
I changed the cell format to "hh:mm AM/PM" It's ok with me. But there is no way to give me the result without (AM or PM). I mean for example 15:33 this will change automaticly to 01:33, for more example:
- From 15:00 to 03:00
- From 19:48 to 07:48
- From 18:20 to 06:20
- From 21:00 to 09:00
- From 13:15 to 01:15

Could please help me urgently.

Thank you

Mostafa Saqallah

Please, there is no anyone can help for the above mentioned. This is very important for me.
I need urgent help please.

Thank you.