Remove Style on Element

You can edit style with pure Javascript. No library needed, supported by all browsers except IE where you need to set to '' instead of null (see comments).

var element = document.getElementById('sample_id');

element.style.width = null;
element.style.height = null;

For more information, you can refer to HTMLElement.style documentation on MDN.

var element = document.getElementById('sample_id');
element.style.removeProperty("width");
element.style.removeProperty("height");

Use javascript

But it depends on what you are trying to do. If you just want to change the height and width, I suggest this:

{
document.getElementById('sample_id').style.height = '150px';
document.getElementById('sample_id').style.width = '150px';


}

TO totally remove it, remove the style, and then re-set the color:

getElementById('sample_id').removeAttribute("style");
document.getElementById('sample_id').style.color = 'red';

Of course, no the only question that remains is on which event you want this to happen.

Update: For a better approach, please refer to Blackus's answer in the same thread.

If you are not averse to using JavaScript and Regex, you can use the below solution to find all width and height properties in the style attribute and replace them with nothing.

//Get the value of style attribute based on element's Id
var originalStyle = document.getElementById('sample_id').getAttribute('style'); 

var regex = new RegExp(/(width:|height:).+?(;[\s]?|$)/g);
//Replace matches with null
var modStyle = originalStyle.replace(regex, ""); 

//Set the modified style value to element using it's Id
document.getElementById('sample_id').setAttribute('style', modStyle); 

$("#sample_id").css({ 'width' : '', 'height' : '' });