Essentially it will be the same as the Nuptial Mass. I (relatively) recent times I have played the organ at a Golden wedding anniversary Mass and at a Silver anniversary Mass which was for my parents. You will be able to choose readings which are especially appropriate for the special occasion. These are the readings which were used in both of the Masses: Sirach 6: 14-17; Tobit 8: 4-9; Proverbs 31: 10-31; Corinthians 13. Of course there are many more suitable readings, although it is perfectly fine if you would rather use the readings and psalm of the day.
At the Mass for my parents, their wedding rings were brought to the altar to be blessed after the homily. Then my parents went to the altar and renewed their wedding vows and then the rings were blessed. As in their first wedding they exchanged the rings and then they lit a wedding candle to symbolise their continued unity in marriage.
The liturgy of the eucharist is as normal, but after the Our Father, the priest may give the Nuptial Blessing. The final prayers can also be taken from the Nuptial Mass - “May God, the eternal Father, keep you steadfast in your love…May the peace of Christ ever dwell in your home. May the angels of God protect it and may the Holy Family of Nazareth be its model and inspiration…” As LilyM said, you will have to alter certain parts to reflect the fact that these people have already been married 50 years, and that they are commemorating that by renewing their commitment to one another - it’s not another marriage!!