Open Product edit page of any Product on which you want to use image or color select and choose variable product. Upon selection of variable product you will see an extra tab with name "variation select".

If you haven't added attributes and setup variables then visit first attributes tab and set up attribute like this.

And then visit variations tab and setup variation product and then update the product. Make sure you have set the 

prices for variations and after updating product , variable product works with default dropdowns. 

Now visit variation select tab and click on the attribute to configure its display.

To replace default select you must select color or image for display type. Selecting none will display default dropdown select.

select display size and other display related option next.

Now click on each attribute value to setup color or image for each attribute.

Done. now open product to test everything from front-end