An upgradable radio-over-fiber (RoF) transport system is proposed based on a vertical-cavity surface-emitting laser (VCSEL)-composed wavelength selector. The passband window of the wavelength selector can be electrically adjusted to select a specific lightwave from multiple injected optical carriers and attenuate the others. By adding the VCSEL-composed wavelength selector installed inside each base station (BS), the proposed transport system can remain as the original tree topology, but its overall network capacity can be flexibly extended (reduced) by adding (removing) an additional optical carrier into (out of) the optical network. Each BS can dynamically receive data from one of the multiple injected optical carriers. This method is useful because the bandwidth requirement of each BS, which is serviced by an RoF transport system, may significantly change with the visitor flow rate. Experimental results prove that the BSs in the proposed upgradable RoF transport system can be reallocated to multiple logical RoF links and can be dynamically switched to receive data from any one of the logical RoF signals without modifying the original network structure. The transmission performances of these optical carriers are ensured by low bit error rate, clear eye, and optical/electrical spectra diagrams.