One suggestion for you is to try using a browser with developer tools like a recent version of Firefox or IE. Learn to use the Inspector tool to find the information you need about HTML elements, attributes, and CSS rules.
Using this example, if I inspect a delete button from a collection, I get information about the nested heirarchy of HTML elements leading to it:
li#q8.form-q.cf-collection-block > div.cf-collection.clearfix.kx-repeatable > div.form-q > span.cf-collection-delete.selectable.lfi.lfi-times
So here, you can see that my collection (id=q8) has several layers of nested elements, but the important one is the one at the end with the '.cf-collection-delete' class. This tells me I can use the selector below to modify that element (in your case, set display to 'none' to hide it):
#q8 .cf-collection-delete {display:none}
That should do what you want, and hopefully help you to find what you need in the future too.