Table size reduce with help changing collation charset [MySQL]

Question

I have table which is big enough, phpmyadmin shows that it takes more than 40Gb space. I can't remove data from it, but I've figure out one thing: there is one field which is described as

varchar(3) utf8_general_ci

There are always latin symbols.

I thought that changing collation to latin1_general_ci would reduce the Table size.

I've tried this out on small version of it with 200 Mb but I did not get expected result :(

Why so ?