This depends on the company form. In a general partnership, the contract may only be amended by a resolution of the partners' meeting carried by the numerical majority of partners who own three-quarters of the capital, and the amendment takes effect by registration (art. 52). A partner who did not approve the amendment has a right to withdraw; the company values his rights by agreement of the majority of the remaining partners, and if he does not accept that, his rights are valued under the first paragraph of art. 11 (art. 52).
In a limited liability company, amending the contract falls to the extraordinary general assembly (art. 117). That assembly is only validly held if partners owning three-quarters of the capital attend, and its resolutions only pass with the approval of partners owning three-quarters of the capital (art. 116). Extraordinary general assembly resolutions take effect by registration in the commercial register, without needing to be put into an official instrument (art. 117).
This is general legal information, not legal advice. For advice on your specific situation, consult a lawyer licensed in Kuwait.