help!!! suit jacket is too tight at the waist. Do I alter the suit or get a different size?

the sleeves are short, suit waist is tight and pants (came as a set) are too tight. If I get the next size up, 38S (it's a 36S right now and they don't make 36R) can I alter the shoulder width/suit length if too long?

from what I understand, the chest size impacts the length of the shoulders, sleeves, suit, waist etc.but what does short/reg/long impact? will it impact the waist? 

Should I alter a smaller suit or larger suit?