How do I notify HMRC of change in status to newly Self employed

Hi, I was employed previously but was made redundant last month. Now I am setting myself up as Self employed - how do I notify HMRC of this please (is there something I can do online)? Thank you

Hi MKL,
please refer to Working for yourself
Thank you.

Hi, I already submit the annual self assessment as I have other incomes. My question is, how can I notify HMRC of the change in status from employed to self employed in the system please? In the link you suggest it only talks about 'registering for Self Assessment' but I don't need to do that. Thank you

Please ignore, I have created a new thread

Hi MKL,
If you need to register for self-employment as part of your self-assessment you can either register at the link below, call the self-employment helpline or by using your Personal tax account to use our web chat services. If you have not done this already. 
Working for yourself
Your employment will be ended via the P45 and you can discuss any help on how to place your leaving date on your self-assessment with that helpline - 0300 200 3310.
If you need to discuss your employment ending for any issues with your employer, please call the pay as you earn helpline - 0300 2003300.
Self-employed helpline:
Number - 0300 200 3500
Overseas - + 44 191 203 7010
Open - Monday to Friday: 8am to 6pm
Closed on Saturdays, Sundays and Bank Holidays.
Thank you.