The only way, without a calculator, that I know of is long division.
Divide the numerator by the denominator
71.1429
You should be familiar with long division involving decimals
150.4
5/8 = 5 divided by 8 = 0.625
By using a calculator:)
486 divided by 7 with a remainder = 69.42857142857143
4690 without using a calculator !
540... without using a calculator !
480... WITHOUT using a calculator !
Most scientific calculators can do this sort of conversion - including the scientific calculator included in Windows (set the mode to "Scientific" or to "Programmer", depending on the version). If you need help using your calculator, or if you want to learn how to do the calculation without a calculator, ask a separate question about that.
To convert a fraction to a decimal, you divide the numerator by the denominator - on a calculator, or using long division.