Can i disable the auto-save function of FMP5 and create a button so that FMP5 can save changes only when user click the button?

Not directly, but you may be able to fake what you want to do.

It sounds like you want your users to enter data, but not have that data written to a record until they click a button.

If that's the case, create a data entry layout which doesn't actually have the fields of the record that would normally contain information. Instead, it has a global field for each normal field.

When a user wants to edit the data, you use a script with a bunch of Set Field steps to get the data from the normal fields to the global fields. Then you take the user to the layout where they can edit the global fields. If they click a button for "Save", then you use another script to set the global fields' data to the normal fields. If they click a button that says perhaps "Cancel", then you just take them back to the data view layout without bothering about the data in the global fields.

Chuck