All perfect praise be to the Lord of the Worlds and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
The Law-Maker has forbidden selling the kinds in which there could be Riba(usury and interest) in order to preserve the stability of funds and transactions as well as to prevent grave harms resulting from that (Riba). Ubida b. al-Simit (Allah be pleased with him) reported Allah's Messenger (PBUH) as saying: "Gold is to be paid for by gold, silver by silver, wheat by wheat, barley by barley, dates by dates, and salt by salt, like for like and equal for equal, payment being made hand to hand. If these classes differ, then sell as you wish if payment is made hand to hand."{Muslim}.
Gold is a usurious kind of wealth; therefore, it is to be paid for by gold of equal weight, because what counts is equality of gold`s weight in its pure form, not its quality or kind of item. This is due to the fact that Sharia-approved evidence stipulate that the exchanged items be analogous, while it didn`t take into consideration the kind of the item itself, which leads to difference in value.
Al-Imam As-Subki said, "The Law-Maker didn`t take quality into consideration: good or bad quality are the same"{Al-Majmou` Shareh al-Mohazzab,10/70}. The ruling of Sharia in this regard isn`t affected by the difference of quality between old and new gold items because what counts is that the weight of pure gold is analogous and the exchange is made in the same place hand by hand."
In conclusion, it is forbidden for you(asker) to exchange old gold items for new ones of non-identical weight; rather, it is imperative that they be of identical weight. Another correct way is to sell your gold belongings, get the money and then buy a new gold item. And Allah knows best.
