If you are tired of your existing tiles, but don’t want to go to the trouble of removing and replacing them, you could always try decorating them. Specialised tile paint has been available from DIY stores for several years, with the range of colours and finishes increasing all the time. You will need to key the existing tiles first by sanding them, then the paint can simply be applied without a primer or undercoat.
Alternatively, if you cannot find tile paint in the exact colour you require, you can buy tile primer. Once this has been applied to keyed tiles, it allows you to use ordinary emulsion paint over the top. This needs to be sealed with clear sealant to make it waterproof and to increase its longevity.
A third way to spice up tired tiles is to add decorative transfers. These are not so widely available as tile paints, but the larger DIY stores should stock them in a range of colours and styles. A few of these transfers dotted around a plain tiled wall can really make a difference to the appearance.
If painting or sticking transfers to your tired tiles is just not going to do the job, you might be able to tile directly on top of existing tiles. In many cases tiles may be basically sound but perhaps not to your taste. If this is the case, you can simply apply new tiles over the top in the same way you would apply them to a clean wall.
Make sure the tiles you are laying on to are clean and free from grease, etc. If any tiles are loose, remove them and re-fix them properly. Now apply your tile adhesive with a notched spreader to create horizontal ridges. Now start pressing your new tiles onto the adhesive (press them, don’t slide them into place if you can possibly help it). Use tile spacers as you normally would and allow the adhesive to dry thoroughly. Now grout and polish your tiles to finish them off.
In some cases it is simply the grouting which lets a tiled wall down. If this is the case, you can simply re-grout the wall. Carefully scrape out as much of the old grout as possible using an old screwdriver or thin chisel. Then re-grout and polish. You will be amazed at how much difference a simple job like this will make.