Grambo - you said it buzzes in the higher frets. Around what fret does it start buzzing? If it's before the 12th fret or so, it is probably a truss rod adjustment. If it is above the 12th fret, it may need a fret leveling job (not uncommon with Squiers). A shim is normally only used when you are unable to raise or lower the bridge any further using the adjustment screws on the saddles. A shim should be your last course of action, as it will likely [slightly] alter the sound and playability of the guitar.