It is not necessary to make a formal conversion. You can simply make an inner commitment to follow and respect Imam 'Ali and the other Imams, to implement the teachings of the Prophet (S) as transmitted from the family of the Prophet (S) (that is, Shi'i hadith), and to follow Shi'i religious law.
In practice, you will probably also want to find a Shi'i mosque or Shi'i gatherings to attend, if it is possible where you live. (It isn't a requirement, but most people like to spend time with people of the same faith orientation.)
There are a number of recommended practices in Shi'ism that are not required while, at the same time, are spiritually beneficial, such as reciting certain du'as on certain days, such as Du'a Kumayl on Thursday nights. One can find more information on these things on the websites www.duas.org. Attending gatherings for these can also be both spiritually and socially beneficial, although they are not considered necessary in the same way the salat is necessary.
In terms of deepening one's knowledge of the Shi'i tradition, there are a lot of good videos on YouTube and on sites such as ShiaTV.Net as well as sites from mosques (for instance, broadcasting Friday sermons), and also a lot of books available, including on al-islam.org.
[Note that I am putting these resources for information only, not implying that you do not have knowledge of these subjects already! However someone else might come across this response and find the links useful.]