“My first performance wasn’t the best, but that’s what I’m like, I go back to the drawing board and showed what I’m really capable of,” said Shittu.
“Credit to my opponent. He was game, he was strong, but ultimately skills paid the bills, booked me a place in the semi-finals and a guaranteed medal.
“Last time I brawled, now I want to show that I can box. And the end of the day it’s hit or not get hit. So I went out there, put on a show. Got the medal, let’s go change that colour.”
Makin, a bronze medallist at last year’s World Boxing Championships, won 3-2 against Armenia’s Marat Mikaelyan.
The 22-year-old will face Azerbaijan’s Saidjamshid Jafarov in Thursday’s semi-final.
The remainder of Great Britain’s fighters experienced defeat on Wednesday, with Lauren Mackie and Amy Broadhurst both losing in the quarter-finals.
Commonwealth Games bronze medallist Mackie lost 5-0 to Lenka Bernadova of the Czech Republic in the women’s bantamweight division, while Broadhurst was beaten 4-1 by France’s Sthelyne Grosy in the women’s lightweight.
Abdul Burton also represents Britain on Thursday, facing Turkey’s Semih Gumus in the men’s super-bantamweight semi-finals.
He and Shittu compete in the session starting at 11:30 BST, while Makin’s bout with Jafarov is among the fights scheduled from 16:00.