Press the DISENGAGE button (#25 on the attached image), to disengage the autopilot.
You can also use SHIFT+9 to bring up the 2D autopilot panel.

The autopilot control panel on the 757 is shown below...



From left to right:

F/D on off switch
A/T arm and off switch
EPR select button
White button - speed intervention. Notice the white circle with four lines - these are all speed modes
LNAV and HDG are direction modes
V/S and ATL control up and down.

As shown above, I'm in SPD mode with 244 knots selected, flying a 030 heading, climbing 500 FPM to 10,000 feet using the LEFT autopilot.

If I want to change from HDG to LNAV just push LNAV the autopilot will attempt to track the magenta line. If you wish to come out of LNAV you can select HDG again or track a radio mode signal with LOC. Heading select is different from HOLD. The HOLD button will hold the heading at the moment of button push. To engage heading select you right click on the little black button SEL.

If you want to go back to LNAV, just select LNAV and the autopilot will go back to tracking the magenta line. Same for the altitude modes. You can select V/S and dial in a rate of climb or descent to the altitude in the ALT window. VNAV is also a altitude mode and a speed mode. The number selected in the ALT window is the controlling number. That is why when in VNAV it will remind you to reset the altitude in the MCP.

Each autopilot is the same, so you can select any single autopilot and it will work the same they just have different hydraulic sources. You can disconnect the autopilot with the disengage bar or the red button on the pilot's yoke.

Lou


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I believe I DID answer your question!

You were in LNAV and the plane started a turn which you did not want to happen!

Pressing LNAV again and again gives you LNAV! You cannot turn a mode OFF by pressing the same button, you need to select another mode  

Here is what you can do...

Tip:Pilots always sync up the heading bug, or cement block, with the current track while in LNAV that way if the plane starts to go where you don't want it to go you can press HDG and fix the problem.

If the computer is commanding a turn you don't want, either select heading HOLD, or select HDG and dial in the heading you want.
You cannot go back to LNAV until you fix the magenta line in the computer.
By doing the above, you only change the control to the heading, the rest of the autopilot stays the same (speed, altitude).

After you correct the course in the computer and the magenta line looks correct then you can steer the plane onto the magenta line in heading or hit LNAV.

Lou

That is a different question lad! That is not what you asked in all your past posts.

This autopilot does not have CWS (control wheel steering).

The answer is: NO CAN DO!

I was flying into Anchorage with the 757-200 Freigher that I bought 3 days ago, and I dont know how to ILS yet with it, so I was doing a visual, and I set the heading hold, and when I was ready to lign up with the runway, I right clicked the "Sel" knob and would not disengage, I turned off the flight directors and turned them back on, would not disengage, I clicked the Hold button and right clicked sel, still would not disengage, so I had to disengage the autopilot and fly manually

To disengage the autopilot, press the bar below DISENGAGE on the MCP. This lets you gain control of the 757. It does not disengage the A/T, you need to switch off the A/T ARM switch to get your throttle control back.

This was explained to you in this Topic.