How do I change status and what is the EAD validity?

Once you adjust and receive your green card, your previous status will be terminated and you will be a permanent resident.

If your I-130 priority date is current, you should apply for I-485 adjustment of status [green card] application. As long as your F-1 visa is current when CIS receives your properly filed I-485 application, you should be fine. But you cannot retain your F-1 visa status simultaneously with a pending I-485 application. I will suggest you simultaneously apply for EAD work authorization with your I-485 even if your OPT derived work permit is still valid.. Here is why, You do not have to pay an additional fee for the EAD since it is already included in your I-485 application. Next, there may be restrictions on an OPT derived work permit that does not apply to a work authorization based on an I-485 based application.

You remain in your current status until it expires or until you receive adjustment of status, whichever is earlier. If your current status expires before your I-485 is adjudicated, it will not disqualify you from adjusting status and you will not be considered accumulating unlawful presence - unless your I-485 gets denied, in which case you will be considered an overstay from the date of expiration of your F1-OPT. You can continue working with your OPT employment authorization card until it expires (or until you receive a green card and no longer need an EAD to work). You should also file I-765 application for employment authorization with I-485: this way, you don't have to pay the I-765 filing fee, and, in about 3 months from filing, you will receive a new EAD bearing the "adjustment of status applicant" codes. It will be valid for a year, can be extended if your I-485 will remain pending 9 months from now; and you can use it either right away - or after your OPT EAD expires. A bit of advice: if USCIS does not call you in for an adjustment interview by the time when you will have only a couple of months left of your OPT, or if you have some other reasons to doubt that your adjustment of status will be granted before your current status expires, talk to an immigration attorney about a possibility to extend your F1/OPT status or to change it to something else - to keep you in status regardless of the outcome of the adjustment process.

You will remain in F-1 status until your I-485 is approved. You should also be receiving a new EAD card based on your pending I-485. A new I-765 should have been filed with the I-485 as it was included in the fee you paid. You can continue to work on that new EAD once you receive it. You should schedule an appointment with an experience immigration practitioner if you wish to learn more about the specific time frames.

You can continue working pursuant to your OPT EAD but as part of your I-485 you can also apply for a EAD that is part of the I-485 application and the filing fee is already included so you might as well do that and have the EAD that is not based on F-1 but based on I-485. Please let me know if you have any additional questions or how I can be of further assistance to you in this matter.