Issues Setting up my Shopify Coding and Product deletion

Hi Shopify Support,

I am relatively new to Shopify, I have some questions on some issues that I am having already, please if you can help me with them.

I started with the Brooklyn Them for my store, which was setup for me by a friend but it isn’t working out for my store. So now I am trying to set it all up by myself using the Debut Theme which I prefer.

My questions are:

How do I change the collection titles?
I currently have this for my navigation.

I want to delete the whole COLLECTION TAB as it is the same thing as what’s in the shop tab.
And on the SHOP TAB, some pages that I want to delete as well like the whole ACCESSORIES page and this includes all the images as well.

My worry is the codes. I know nothing about coding.

My other question is what is the best IMAGE SIZE for PRODUCT.

Lastly for I have two Shopify store one is active and the other one isn’t, but I want to transfer my current ownership to the inactive one please is there away this can be done.

I am desperately in need for someone’s help with all this problems. Please your help is needed. Thank you