There are not really four yogas, or rather - there are four ways of working towards removing ignorance of separation (dualism). Once ignorance is seen as ignorance, then no ways are needed, and thus, there is only on yoga (union) which is seeing that no yoga is needed.

As it’s popular following Ramakrisha to distinguish four ways of thinking about the preparation steps, we offer pointers here to the four basic categories -

Karma

Jgani

Hatha

Bhakti