Best Approach for Product Specs Options from Select Selection to Multi Selection

I would like to know the best approach to convert or modify the "Edit Product --> Specification attributes" section to a Multi-Select feature. So that I can pick several attribute options at one time when adding / editing a product. This will help my admins when we have several options to pick for each product.

Here is an example. My list will have sometimes about 40 items to select.

Moving to Commerical Jobs