To change it to hexadecimal, first you have to change it to binary.
Octal - Binary:
To change it, first have the digits of an octal be divided to 1-digit numbers. Have 4,2,1 on the top of each digit. If the number is not included to total a number, cross it out; it's 0. If it was one of the digits that adds up a number, it's 1 in binary mode. For example: 356; the binary of it is 011 101 110. Remember: The numbers for octal is only up to 7, since 4,2,1 is the only digits for octal.
Binary - Hexadecimal:
To change it, divide the binary into 4 digits from the right. Put 8,4,2,1 on it. If the digit above aligns to 0, cross it out, but let the digits with 1 on the below of it. Add all the numbers above which is uncrossed. If the number exceeds to 10, the values would be A,B,C,D,E, or F depending on the number of 2-digits (note that it's only up to 15, since 0 is included). Example: 001100101010 = 32A₁₆. Don't forget the 16 sign to denote a hexadecimal.