Redemptionis Sacramentum says...
If you want to kneel, you may kneel
Here is the relevant guidance from the Congregation for Divine Worship and the Discipline of Sacraments contained in Redemptionis Sacramentum, issued in April 2004:
“In distributing Holy Communion it is to be remembered that ‘sacred ministers may not deny the sacraments to those who seek them in a reasonable manner, are rightly disposed, and are not prohibited by law from receiving them.’ Hence any baptized Catholic who is not prevented by law must be admitted to Holy Communion. Therefore, it is not licit to deny Holy Communion to any of Christ’s faithful solely on the grounds, for example, that the person wishes to receive the Eucharist kneeling or standing.”(Emphasis added.)
“Although each of the faithful always has the right to receive Holy Communion on the tongue, at his choice (emphasis added.), if any communicant should wish to receive the Sacrament in the hand, in areas where the Bishops’ Conference with the recognitio of the Apostolic See has given permission, the sacred host is to be administered to him or her...”
To read Redemptionis Sacramentum in its entirety from the Vatican website: