Hi there Irinel,
Phil from the Shopify Support team here. Thanks for your post and welcome to the Shopify Forums.
When it comes to collections URL you're talking about you currently can not change that bit. No matter what, before the name of the collection or in any collection URL, 'collections' must be in the URL prior to the name of the collection you are linking to. This is Shopify's URL structure, and that is how our development team decided for it to be structured. The reason 'collections' is found before the name of the collection is to tell the system you're calling on that collection.
You can't rework this URL. You can adjust the text after the word 'collections'. To do this all you need to do is go to the collection in your admin, scroll to the bottom and click the 'Edit Website SEO' button. You can adjust it to whatever you want but everything from the word 'collections' and before is non editable because this is Shopify's URL structure.
I hope that clarifies your question!