end game
Do some of the basic endgame drills here.
https://www.chess.com/drills/endgame-fundamentals
Study an endgame book. There are many and some are aimed at intermediates.
I have one from Bruce Pandolfini that isn't too bad. (Pandolfini's Endgame Course).
Jeremy Silman also has one.
There are also endgame lessons here in the Lessons section.
No one is going to open up your head and pour the knowledge in. You have to go get it through study.
Various endgame study possibilities discussed at:
https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review594.pdf
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
https://www.newinchess.com/media/wysiwyg/product_pdf/7742.pdf
https://www.chess.com/article/view/book-review-winning-chess-endings
https://web.archive.org/web/20140708105702/http://www.chesscafe.com/text/review645.pdf
https://www.newinchess.com/media/wysiwyg/product_pdf/9026.pdf
http://chessimprover.com/averbakhs-chess-endings-essential-knowledge/
https://web.archive.org/web/20140708234309/http://www.chesscafe.com/text/review704.pdf
http://www.gambitbooks.com/pdfs/Understanding_Chess_Endgames.pdf
http://theweekinchess.com/john-watson-reviews/endings-endings-endings
http://theweekinchess.com/john-watson-reviews/the-end-game-comes-before-we-know-it
http://theweekinchess.com/john-watson-reviews/theres-an-end-to-it-all
Before buying any particular book, I suggest going to the publisher site to see if it is possible to view a sample.