Here's what can help you buddy.

In order to convert from decimal to hex you'll need to do this:

x=(x % 10) + ((x/ 10)<<4);

where x is the variable which contains the number in decimal.

when you read back from the RTC the hex value will be read and you'll need to do this in order to convert it back to decimal from hex:

y=(y & 0x0F)+((y>>4)*10);

here y is the variable which contains the hex value and will be converted to decimal so that you can display it.

cheers