Although other software might open the file, only Photoshop will retain its full functionality, especially the layer styles. Using other tools may result in a loss of texture detail, as you'd have to rely on the paint bucket tool. In this guide, we'll retexture a polo shirt.
When you open the psd file, locate the "Colour" layer near the bottom. Click the drop-down arrow beside it to reveal its effects. Double-click "Color Overlay" to open its menu. Here, double-click the black square and enter your desired hex code.
Repeat this for the "Undershirt" and "Sleeves" layers.
To update the text to match your department, use the text tool. Simply click on the text and make your changes.
For changing the patches, use File > Place Embedded or drag them in from your file explorer. Once the patch is in, use the box controls to resize and position it over the existing patches. Then, enable the "Template" layer to ensure nothing extends beyond the edges of the decal, as this will not be visible in-game.
If you notice white outlines around the patch in-game, create a black fill layer at the bottom of the psd file and set its opacity to 1%.
In this guide we used the psd file for the Polo Shirt but these same steps will work on any psd.