this is solution to let slideshow support horizontal align not just center as of version 2.3.0.
you have to modify 4 files in plugin. first go to the template directory.
in the all 3 temlate files in ‘template’ directory find this code:

<th scope="row">Center whole slideshow</th>
                <td><select name="advps_centering">
                	<option value="no" <?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'no'){echo 'selected="selected"';}?>>No</option>
                    <option value="yes" <?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'yes'){echo 'selected="selected"';}?>>Yes</option>
                  </select></td>

and replace with:

<th scope="row">Align whole slideshow</th>
                <td><select name="advps_centering">
                	<option value="left" <?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'left'){echo 'selected="selected"';}?>>Left</option>
                    <option value="center" <?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'center'){echo 'selected="selected"';}?>>Center</option>
					<option value="right" <?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'right'){echo 'selected="selected"';}?>>Right</option>
                  </select></td>

in all 3 templates.

next in file ‘advanced-post-slider.php’ find this code:

<div id="advps_container<?php echo $sldshowID;?>" class="advps-slide-container" style="overflow:hidden;max-width:<?php echo $container['advps_sld_width'];?>px;<?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'yes'){echo 'margin:auto;';}?>">

and replace with:

<div id="advps_container<?php echo $sldshowID;?>" class="advps-slide-container" style="overflow:hidden;max-width:<?php echo $container['advps_sld_width'];?>px;<?php if(isset($container['advps_centering']) && $container['advps_centering'] == 'center'){echo 'margin:auto;';} else if (isset($container['advps_centering']) && $container['advps_centering'] == 'right') {echo 'margin:0 0 0 auto;';}?>">

save modified files.
go to the slider options and now you see align options: left, center and right available.