Shower drain repair or replacement may not be necessary if your problem is as simple as a slow draining shower. The most likely reason for a shower to drain slowly is because of a clog somewhere down the drain.
Shower drains are generally fairly easy to remove in order to use a plunger. In fact, many shower drains won’t need to be removed at all. However, if you have a bath/shower combination, it is likely that you have some kind of stopper attached to your drain. This should be removed before using your plunger in order to get the most effective action from the plunger.
There are different types of stoppers and you will need to know what kind of stopper you have before you know how to remove it. The easiest to remove are those without a trip lever attached. Generally these can be removed by loosening or removing a single set screw. Models with a trip lever are going to be more complicated to remove as the entire lever assembly and drain may need to be removed. On the bright side, this is a good time to make sure that all the parts are in good conditioned and lubricated before you reassemble.
Once you can create suction with your plunger and there are no obstructions in the way, you should be able to clear the clog quickly. Keep in mind that you may need to stop up the overflow drain if you are working with a bath/shower combination in order to create enough suction between the plunger and the pipes to move the clog.
If the drain is still slow, does not seem to be draining at all or you notice a visible leak, shower drain repair may be necessary. Simply call a licensed professional plumber to diagnose the problem and fix it properly.