Percentage of owners needed to sell part of land

I’m going to quote the relevant section of the Act (S.116) below because it is a little confusing. On the one hand, it appears to allow the Owners Corp to sell its property.  On the other it says OCs are not subject to Section 50 (1) (d) of the Interpretation Act 1987  which … allows OCs to sell common property.
You are going to have to consult a strata lawyers at some point on this, so hopefully they will clarify this for you. On the face of it, it looks like you can sell common property and it would only require a special resolution.
However, there is a catch. The capital gain from selling the property may be taxable for individual owners. For example, your strata manager may have to distribute the value (but not the cash) to every owner according to their unit entitlements, with the expectation that they will include this in their tax return.
However, the money gained can only be distributed to owners via a unanimous resolution (no votes against).  Otherwise it stays in funds where it can be used for repairs and maintenance or to finance a reduction in levies.
All that said, disposing of unused common property is a good way of funding repairs and upgrades – just be aware of the tax implications.

116   Powers to deal with property

(1)  An owners corporation may dispose of or otherwise deal with any lot vested in the owners corporation as a result of a subdivision effected under section 13 of the Strata Schemes Development Act 2015.

(2)  The owners corporation may acquire or dispose of personal property or otherwise deal with personal property of the owners corporation.

(3)  Section 50 (1) (d) of the Interpretation Act 1987 does not apply to an owners corporation.

Note—

Section 50 (1) (d) of the Interpretation Act 1987 provides that a statutory corporation may, for the purpose of enabling it to exercise its functions, purchase, exchange, take on lease, hold, dispose of and otherwise deal with property.