On a pencil and paper standardized test,within ant given section of your test book let you are free to skip from question to question and to answer questions in any order you choose.if you do better on antonyms than on reading comprehension questions, for example you can temporarily skip the time consuming reading passages and go straight to antonyms.
Like wise, if you have second thoughts about a particular answer choice on a pencil and paper test you can go back to the questions ,erase your original pencil mark and select a different answer choice.you are also free to write in your test booklet,crossing out incorrect answer choices,under lining keywords and highlighting question you need to re-consider.
On a computer based test,there is no test booklet.your test questions appear one at a time on your computer screen.You must answer the question currently on the screen and confirm that you are sure of your answer choice before you can move on to the next question.Once you have confirmed your answer choice and moved on, you cannot go back and change it.