I'm assuming that it is clear to you that a vocation to the religious life is not synonymous with choosing a career. Rather it is a call of God. With this in mind I will answer your question by making the distinction between the primary reason that should motivate you and the secondary conditions that may be required.
"The gift of religious vocation is rooted in the gift of baptism but is not given to all the baptized. It is freely given and unmerited: offered by God to those whom He chooses freely from among His people for the sake of His people." (Essential Elements of Religious Life. p 45) This means that God calls whomever He wills and whenever He wills. Discerning that call and responding to it generously is the primary reason for choosing to join a convent regardless of whether or not you have a college degree.
These conditions differ first of all depending upon the apostolic work of the Congregation. Let me explain: a teaching Order, for example, would most likely accept candidates who are teachers or have a strong inclination or love for teaching. I would assume this to be true of the candidate who is searching for a place to serve in response to the call of God in her life. Likewise, if the work of the Congregation happens to be running hospitals, nursing homes, health care facilities and the like, the members would need to have some proficiency in the medical field. Practically speaking, you need to have the tools to do the job.
Although these educational qualifications may not be necessary before you enter the convent, training would be needed after you join.
All religious communities have a period of intense formation for new candidates and on-going formation for all its members. So, you can see that study is an important aspect of religious life.
Secondly, these conditions differ depending upon the Congregation's basic requirements for accepting new members. They could include any or all of the following: That you be debt-free, single, emotionally and psychologically stable, free of canonical impediments, physically able to live the life, and so forth.
To join our community you would need to have a high school diploma as the minimum educational requirement.
Because God calls us at different stages in our lives; whenever He wills, my advise is that as soon as you are aware of the possibility that God might be calling you, speak to the vocations director of your diocese or someone who can give you solid spiritual guidance. By taking this important step you will gain clarity in the process of discerning God's will and of making practical decisions about His specific plan for your life.
Sister Rita, DLJC