Question

How to change a sentence from active to passive

Answer 1

Simple rewording.

An active sentence would be:

The dog bit Mary.

"The dog" is the subject, "bit" is the verb, and "Mary" is the object being acted upon.

A passive sentence would be:

Mary was bitten by the dog.

The sentence is basically reversed. "Mary" is still the object being acted upon, but it comes first. "The dog" is still the subject performing the action, but it comes last.

Answer 2

You can always know that the way it is usually passive is if it has -ed but a way to change it is if you: Follow this:

STEP 1: move the object to the subject position

The report ...

STEP 2: change the verb to the passive, making sure that BE takes the same tense as the verb in the active sentence

The report will be presented ...

STEP 3: drop the subject

Example of passive voice without the subject 
The report will be presented next week.

or move it to a position after the verb

Example of passive voice with the subject 
The report will be presented by the group next week.