Hi,
The block "Specifications" is generated if you are using Custom Fields, and the HTML on the linked product page is showing that you are having at least one custom field of the type "product" published and assigned to this product.
Now, on one hand you say you want to (completely?) remove the whole block.
Which is simple - depending on what you really want, just delete the custom field, or unpublish it from the frontend, or do not assign it to or use it for the particular product, or generally deactivate the display of custom fields in configurations.
Then you say you need to replace it with your own specifications (= custom fields)... so, I guess not remove it?
Well, then create and publish custom fields of the type "product" and assign/display them as per your liking.
More on custom fields - as usual - in the documentation:
hikashop.com/support/support/documentati...shop-field-form.html