Probably the single most confusing area of the Liturgy of the Hours involves knowing what your choices are on memorials of saints. I get asked about this a lot. Feasts and solemnities are easy--you do whatever it says for each of these days in the proper of saints, with no variation.Observing them is obligatory. There are some questions about whether to use an Evening Prayer I on their vigil, but that is another topic. The problem with memorials is that there are several ways to do them. Your breviary actually explains this but it means locating the page of explanations and finding the answer to your specific question. It might be easier to copy and print the following general principles and paste them inside the cover of your book.
1. Memorials and optional memorials are celebrated in the exact same way EXCEPT that the optional memorial is optional. This means you may ignore it and just do the current weekday if you prefer.
2. There are two ways to celebrate memorials: a. Stick with the current weekday in your 4-week psalter, substituting whatever variations are supplied in the proper of saints. Most of the time this is only a concluding prayer, but sometimes it can be more, so always look over the entry in the proper of saints before you begin. b. Instead of the weekday in the psalter, choose one of the Commons (holy men, holy women, martyr, etc.), which you use for the entire office, except for those items in the saint's proper.
That's all there is to it. No matter what the St. Joseph guide or anyone else may tell you, you are always free to do memorials in one of two ways. (Or not at all when it's optional)
One more thing. Although many memorials have nothing "extra" other than a concluding prayer, always look at the proper of saints before you start. Some of the more ancient, time-honored saints have lots of stuff in their proper. We have a few examples in July: St. Mary Magdalene; St. Anne&Joachim.
The reasoning behind the Church's giving us these options? It seems that the Church has a kind of "preferential option" for the four week psalter and the normal yearly sequence of scripture readings in the Office of Readings. She does not want us to lose the rhythm of the psalter, nor miss too many of the appointed daily bible readings, which is what would happen if we celebrated every single memorial using the commons for saints. At least, that is how I understand what I see in the Vatican II documents on the liturgy.