im around 176cm to 178cm. What sized frame should i get?

55cm traditional bikes.
modern bikes something sized a S or M, depending. alternately they might be a 53 or 54.

Try out a 54 and see how it feels, from there you can either go up to a size 56 or down to a 52.

I'm 6'1" (186cm) and I ride a size 58.

I'm 178. I usually ride a 54.

54. You should be perfect as they come. But a stem is easy to swap. A tad too small a frame is an EASY fix. Too large, not so much.