A constitution amendment is any change to the rules that govern your organisation: its objects, its membership classes, the composition and powers of the committee or board, the conduct of general meetings, the financial year, or the treatment of assets on dissolution. Under Singapore law a society's rules, a charity's governing instrument and a company's constitution are all binding internal contracts, so no change takes effect simply because members want it. It takes effect only when passed by the required majority and, where the law demands it, approved or registered by the relevant authority.
A special resolution is the elevated voting threshold reserved for these constitutional changes. For a company limited by guarantee under the Companies Act 1967, a special resolution needs at least 75% of the votes cast by members entitled to vote at a general meeting, on proper written notice. Societies set their own threshold in their existing constitution, which is frequently a two-thirds or three-quarters majority of members present at a general meeting, and that internal rule must be followed to the letter. The distinction matters because an ordinary resolution, even a unanimous one, cannot validly amend a constitution where the document or the statute calls for a special resolution. The voting record you keep is the evidence the regulator will scrutinise, so it has to show the precise figures, not just an outcome.