Of course, officially, for giving false testimony against a witness is a punishable offence, as well as for refusal to give testimony. And before any interrogation you should know about this responsibility and to clarify your rights and responsibilities. But even the law provides exceptions that allow you to refuse to give testimony. For example, nobody can force you to testify against himself or his relatives.
If you have already given testimony, and then I wanted to give others or even to abandon them, it will automatically mean that in one case, your statement was false, so theoretically you may be brought to criminal responsibility.
But in practice it is not uncommon when a witness gives false testimony. And in very rare cases this is followed by criminal liability. It is rather insurance "horror story" for adults. So if you change your testimony, the court has the discretion to use any of the information, both primary and secondary.
To give new testimony or to opt out of the indications, wait until you will again call to give testimony. In most cases, this procedure is repeated several times. If the case is in the investigation process, then you certainly will be asked to come. You can, of course, themselves to take the initiative. Will request on an unplanned visit to the authorities, where he gave earlier testimony. And being already in place, notify us of your decision to abandon is made of the testimony.
Most likely, you will be required to explain the reason why you decided to refuse from testimony. In this case it is better to consult with a lawyer, what should you do and what to say. Because for every case and trial is an individual right.