the left part is big seal script for character "Book"
because 2000 years ago, people wrote on bamboo or wooden slips, so book was formed by many slips connected by rope, which is the left part. There was no eraser at that time, if people wrote wrong, they used knife to scrape the surface for rewriting. So "a book + a knife" means "delete".
The person who is responsible for writing documents has brushes and a specific small knife for deleting the wrong characters on bamboo slip. People called him " 刀笔吏", officer of knife and brush.
The character is formed by two other pictography characters to express a different meaning, which is an ideogram character.
Its small seal script is
very similar to the big seal script.
Its clerical script is
changed a lot on both parts, especially the right part "Knife", which is a short vertical line plus a vertical line with a hook at the bottom, not like knife very much.
The current standard printing script for traditional character is
The current standard printing script for simplified character is
The difference is very small, actually they have the same number of strokes, which means there is no any simplifying.
I need to point out that 删 could mean "Erase" too.
Its Pinyin is "Shan1".