Replacing Textures and Armor Title Problem

I dont know why but when i try to replace a texture with a new one it keeps getting me "There is allready a texture with that name! to enshure no data lost rename the new texture pack" or something like that... But if i dont want the old one because it keeps getting in my way? Theres no option to do that sadly whats a pain... Also that you cant delete them from texture libary  (the section from where you pick or insert new textures for making an item etc) 

Also next problem its because of the first one that you cant replace or delete textures. When ive made an armour pack it made automatically an armour what ive didint wanted and took my name for a armour pack... because of that ive needed to rename because of no replacement option my armour in over simmilar name. okay maby simmilar name isnt bad but i think that having "_" sign at end of basic name of the armour pack really hurts my eyes as also it isnt estethic.

If someone could say whow from where you can delete the imported textures as i think their might be a way fro files but when ive tried to find i didint...