Certain cosmetic upgrades (like painting) may not require board permission but it is best to check in with management before starting any work in your unit.
Contact the co-op's managing agent, who can provide the building's alteration agreement, which should outline what kind of jobs require approval, licensing and insurance requirements for your contractor, potential fees, security deposits, work schedules, requirements for use of the building's service elevator, requirements to file with the Department of Buildings, and other pertinent information.
If you're still unsure about your planned upgrades, write a letter to the board describing the proposed work and ask the board whether any consent would be required.
Depending on your building, you may not need permission for cosmetic work that does not involve major systems like electrical or plumbing, but some co-ops have a decoration agreement. The decoration agreement does not require board approval for paint and floor work and minor cosmetic things but it does require that the contractor is licensed and insured and that the insurance names the co-op as one of the insured. For smaller jobs, the work is usually approved by the managing agent and then coordinated with the building. This small-scale approval process should not take more than a few days.
Ask the managing agent, if you are still unsure about your planned work, and they should provide you with all the information you need.