It's wonderful to see that you're planning a surprise for your wife's anniversary by expanding her favorite pair of heels. Here's a detailed answer on how to use shoe stretchers effectively and safely:

 1. Choose the Right Shoe Stretchers: When purchasing shoe stretchers, ensure they are designed specifically for the type of shoes you want to stretch. There are various types available, including wooden, plastic, and metal stretchers. Consider the material and shape of your wife's heels to select the most suitable option.

 2. Prepare the Shoes: Before using the stretchers, clean the shoes thoroughly, removing any dirt or debris. You can use a soft cloth or brush to wipe away any dust. This step ensures that the stretching process is done on clean shoes.

 3. Insert the Shoe Stretchers: Gently insert the shoe stretchers into the heels, making sure they fit snugly. Ensure that the stretchers are positioned correctly, aligning with the shape of the shoes. It's crucial to be gentle during this step to avoid damaging the shoes or causing any unnecessary strain.

 4. Adjust the Stretchers: Most shoe stretchers have adjustable components to allow for customization. Carefully adjust the stretchers to gradually expand the shoes. Begin by turning the adjustment knobs or screws slowly, allowing the stretchers to apply gentle pressure. It's essential to be patient and not rush the process, as sudden or excessive stretching can damage the shoes.

 5. Monitor the Progress: Regularly check the shoes to monitor the progress of the stretching. Leave the stretchers in the shoes for at least 24-48 hours, depending on the material and desired stretch. During this time, the shoes will gradually expand, accommodating your wife's feet more comfortably.

 6. Repeat if Necessary: If the initial stretching is not sufficient, you can repeat the process by adjusting the stretchers further. However, it's crucial to be cautious and avoid overstretching, as it may result in irreversible damage to the shoes.

 7. Test the Fit: After the desired stretching duration, carefully remove the shoe stretchers and try on the heels. Encourage your wife to wear them and assess the comfort level. If they still feel slightly tight, you can repeat the stretching process until they fit perfectly.

 Remember, each pair of shoes is unique, and the stretching process may vary depending on the material and design. It's always a good idea to refer to the instructions provided with the shoe stretchers you purchased, as they may offer specific guidance tailored to the product.

 In addition to using shoe stretchers, you might also consider using stretching sprays or employing professional shoe stretching services if needed. These options can provide additional flexibility and ensure a comfortable fit for your wife's favorite pair of heels.

 Overall, your thoughtful surprise of expanding your wife's favorite heels demonstrates your consideration and effort to make her happy. Good luck with the stretching process, and I hope she will be thrilled with the result!