Keep dividing the number by 16 until the remainder turns out to be 0, then write the remainders from bottom to top.

For example we need to change the number 374512 into hexadecimal with base 16, so we proceed as above, then we write those from bottom to top, then change them into respective numbers/alphabet using the chart below. And at last we enclose them into bracket with base 16.

We write the remainders as 5 11 6 15 0
Changing this to respective numbers/alphabet we get 5 B 6 F 0
Enlose this within a bracket with base 16.
So, finally we get: (5B6F0)16