does anyone know how i could safely shrink some clothes?

in my head i dont think i really know what size i am.. in my most recent order i got like a size 2 top (had the hardest time getting out of it) then two size 6 tops (way too big) and one size 4 (fits ok)

and i got this size S bandeau thingy to wear like if im wearing something see through.. should have gotten a 4.

thennn.. my bcbg order.. i got 2 blazers.. one size xs (fits) and one size S (little too big) why wouldnt i just get them both the same size...?

and dont get me started on jeans.. i have every size up to a 29.