Valve guides should be cleaned as outlined earlier, and checked when valve stem diameter and stem-to-guide clearance is checked. Generally, if the engine is using oil through the guides (assuming the valve seals are OK) and the valve stem diameter is within specification, it is the guides that are worn and need replacing.
Valve guides which are not excessively worn or distorted may, in some cases, be knurled rather than replaced. Knurling is a process in which metal inside the valve guide bore is displaced and raised (forming a very fine cross-hatch pattern), thereby reducing clearance. Knurling also provides for excellent oil control. The possibility of knurling rather than replacing the guides should be discussed with a machinist.
REMOVAL & INSTALLATION
Valve guide replacement on all Celica/Supra engines requires breaking off the top end of the guides, heating the cylinder head to almost 200°deg;F (93°deg;C), then driving the rest of the guide out of the head with a hammer and drift. Unless you and your family don't mind baking an oily cylinder head in the oven (and probably smelling it in the house for months), take the head to a machine shop and have a machinist replace the guides.