user6451: I'm actually new to learning the use of After effects but there's a mistake that I did about the keyframes, I should have placed the last keyframe to the first one which I would like to reverse these keyframes simultaneously so that it can possibly do it quickly, is that possible?
Sorry for the unclear words that I have spoken, here's a screenshot showing what I want to do:

Like to place all of those keyframes horizontally reversed to the left so that the first layer will the first one to move.
Thank you!

user6476: If I understand correctly, you don't want to change "keyframes," you want to reverse the order of the images, so that the ones on the top of the stack appear first, followed by the ones below. 
Easiest option: 

Delete the images & comp
Reimport by selecting only the 1st image, and make sure to check the box for "image sequence" this should grab all of them in the correct order & make a comp of the group.

Alternative to avoid reimporting: 

Select all the layers, from top to bottom. 
Hit "Home" to move the Current Time Indicator to 0:00:00
Hit "[" to reset the start of all layers to 0:00:00
With all layers still selected, Right-Click the timeline
Choose "Keyframe Assistant"
Choose "Sequence Layers". Leave "overlap"unchecked. 
Hit Enter

The layers should now be sequenced from top to bottom, the next one starting exactly where the previous one ends. 

user16906: http://www.premiumbeat.com/blog/quick-tip-reversing-layer-order-in-after-effects/
Basically, if you select the last layer first, and then hit shift and select the first layer, then copy them, then delete them, then paste them back in, the layer order will be reversed.

6451: <p>I'm actually new to learning the use of After effects but there's a mistake that I did about the keyframes, I should have placed the last keyframe to the first one which I would like to reverse these keyframes simultaneously so that it can possibly do it quickly, is that possible?</p>

<p>Sorry for the unclear words that I have spoken, here's a screenshot showing what I want to do:</p>

<p><img src="https://i.stack.imgur.com/GuVmd.png" alt="enter image description here"></p>

<p>Like to place all of those keyframes horizontally reversed to the left so that the first layer will the first one to move.
Thank you!</p>
 6476: <p>If I understand correctly, you don't want to change "keyframes," you want to reverse the order of the images, so that the ones on the top of the stack appear first, followed by the ones below. </p>

<p>Easiest option: </p>

<ol>
<li>Delete the images &amp; comp</li>
<li>Reimport by selecting only the 1st image, and make sure to check the box for "image sequence" this should grab all of them in the correct order &amp; make a comp of the group.</li>
</ol>

<p>Alternative to avoid reimporting: </p>

<ol>
<li>Select all the layers, from top to bottom. </li>
<li>Hit "Home" to move the Current Time Indicator to 0:00:00</li>
<li>Hit "[" to reset the start of all layers to 0:00:00</li>
<li>With all layers still selected, Right-Click the timeline</li>
<li>Choose "Keyframe Assistant"</li>
<li>Choose "Sequence Layers". Leave "overlap"unchecked. </li>
<li>Hit Enter</li>
</ol>

<p>The layers should now be sequenced from top to bottom, the next one starting exactly where the previous one ends. </p>
 16906: <p><a href="http://www.premiumbeat.com/blog/quick-tip-reversing-layer-order-in-after-effects/" rel="nofollow">http://www.premiumbeat.com/blog/quick-tip-reversing-layer-order-in-after-effects/</a></p>

<p>Basically, if you select the last layer first, and then hit shift and select the first layer, then copy them, then delete them, then paste them back in, the layer order will be reversed.</p>
