It's not badley built, It's just built low-cost. your grips are probably HARD rubber\plastic, your bars will bend at low-speed crashes, brake pads will wear fast, the suspension is not the best out there, the chain will break after some use, and so forth.
Replace the grips with good renthals, replace the chain with quality one before it breaks, or you can upgrade the sprockets\chain to 428 ones, these are much stronger.
the exhaust will probably have a restrictive weld in the beginning of the pipe, this can be grinded away.
Match the intake manifold to the carb and jet the carb right.
These mods will not make the bike much faster, but will make it crisper and cleaner.