How to fix the low lighting or brightness or dust out inside?

@elsieortiz you mean besides getting to the lamp unit as shown on this guide Sony KDF-E60A20 Lamp Replacement

If so, you are looking into the disassemble of the TV. Use this Sony KDF E60A20 Service Manual and go to page 22 to see how it is done. Careful so you do not run into any issues with the mirror. You can use a microfiber cloths and a brush to remove the dust.

Now, if it is not as bright as it should be, replace the lamp first. If that still does not resolve it, then it could be an inverter issue. Let us know what the exact symptoms are and how you want to proceed.