This is a rather complicated technical process, in which you may need specific knowledge.
It differs a lot for each specific model of phone or tablet.
Moreover there is a risk to permanently damage the device during this operation in case it is fulfilled by non-specialist.
Therefore, we strongly recommend you to apply to the experts for this. It is quick and inexpensive.
If you are familiar enough with computers and phones, it will not be a problem for you to find detailed instructions for your device with the help of an Internet search.