Reply to Blossom - try pruning during winter (from November until February). However, new shoots may not always develop from very old woody stems. Depending on how many thick woody stems it has, it could be worth pruning in stages over a couple of years, pruning some stems back hard this winter and the remaining ones next. Your aim is to encourage new growth to develop from the base of the rose, or from the base of these old stems.
Tying stems down towards the horizontal rather than letting them grow vertically is also recommended. In this way side shoots develop along the length of the stem to provide far more shoots, which in turn carry more flowers.