REPO doesnt change in size

i uploaded a file which had 130 kb. i deleted it. Repository still displays 180kb (why not 130 in the first place).
how to make it 0kb again?

One of the features of git (that GitLab is build on), is that you can get older versions back, so (normally) git doesn’t delete anything.

(A part of) The difference between 130 and 180 is due to metadata.