This is a very common objection that we face as followers as Christ. People will throw this out and we can feel stumped by it.
The first thing we must do is to establish what the person means by this.
Who changed it, when was this and how did they do this? Lastly what evidence do they have for this objection?
This objection is often based on two thoughts:
1) Catholic Church changed the Bible –
Based on the belief that Constantine changed it in 323AD at the Council of Nicea.
This is simply not true, as they met to discuss the deity of Jesus and so called Arianism.
They did not at any point add or remove the 66 books of our current bible. The canon was already well established by this stage.
2) Changed e.g. new Translations –
The Bible has had many Translations these have come about however due to the unearthing of older more reliable manuscripts.
I have added a link on this for more detail.
The Bible has more manuscript evidence to support it, was written nearer the actual events than any other document of antiquity and has been textually criticised as being around 99.5% accurate.