In Aqua Theme, portfolio item page naturally comes with 2 columns. One is for the images Stander one image or gallery depending the choice, the other one is basically the content column which whatever text, bullies, you want to put there. Right now this is how our website looks like: http://bectechnologies.net/portfolio_item/mx1000/

My question is: as you can see, the content part is way longer then the images part. Is there a way I can put the blue “datasheet” button under the image gallery? So the viewer could find the datasheet easier. Thanks.

If you edit your single-portfolio.php template file you will see how it is organized, Image(gallery) to the left and content of the portfolio item to the right…
Since the button is within the bottom it wouldn’t be possible to place it below the Image(s) conventionally. There are several ways to approach this task though.
You could move it with Javascript upon page load (not very nice solution as clients will see a flickering).
You could add a custom field to your custom post type portfolio where you would place your button code, then you would add that custom field front end bit into the template single-portfolio.php below the Images(s).

Look into plugins similar to this:

https://wordpress.org/plugins/wck-custom-fields-and-custom-post-types-creator/

Or you could of course modify your own Portfolio CPT.
Good luck!