Existing Disability Living Allowance claimants are only reassessed if:
From October 2015 all working-age people still receiving DLA will be reassessed and if their claim is successful, moved onto PIP."
You can read more about PIP here.
Just another quick bit of advice, if you click on the following link it will take you to the CAB website which gives more information on how to complete a PIP form. It gives good examples of which boxes to tick depending on your ability to care for yourself and get about/move around. Like others have commented, however, most people are being advised to be extremely cautious about applying for PIP while still in receipt of DLA as the criteria is much stricter: