Adult Catholics that have not received their First Holy Communion are invited to prepare for this sacrament through the R.C.I.A., or Rite of Christian Initiation of Adults. Go to the tab for "Adult Education," then to "Becoming Catholic."
R.C.I.A., while primarily instituted for the un-baptized, is also the process by which Catholics that lack First Holy Communion, or lack BOTH First Holy Communion and Confirmation are properly prepared for the sacrament(s).
Because Catholics in this situation are uncatechized, the Church expects them to be prepared for the sacraments and the commitment of living out their faith along with the un-baptized. The minimum time that this preparation might take place is one liturgical year, but no exact time is predicted up front; it is a process of formation and depends upon the spiritual and moral maturity of each individual.
Catholics lacking only the Sacrament of Confirmation are prepared through the Adult Confirmation preparation.