Please house i need your opinion and or help on how to politely turn down a job offer. I got something more better and i dont want to burn the bridge because of another time.

If i decide to send the a mail ,what could be the content my brain is in a fix at the moment because i wasn't expecting it.

It has to be a formal letter...
Name
Address
Phone number
Date.

To
The HR manager/Dept.
(Name of org.)

Dear Sir/Ma
UNAVOIDABLE INABILITY TO REPORT FOR DUTIES.

...carry on from here. You can give them the excuse of wanting to further or pursue a certain course which admission, came up abruptly or earlier than you expected.