Is it possible to convert USB 2.0 into USB 3.0?
Yes. By replacing the entire usb controller in the device. And the circuit board. And the firmware.

In other words, no. USB 3.0 is not a drop in replacement for USB 2.0.

Now if you need to connect a USB 2.0 device to a USB 3.0 Host, there are two options. The first is a direct connection. 3.0 is backwards compatible, so it can read 2.0 devices at 2.0 speeds. The other option is using a 3.0 hub. USB has Transaction Translators, which can take a slower downstream USB device packets, and interleave them at 3.0 speeds, upstream. Of course, the bottleneck will still exist, it can't magically speed a device up, but it allows a hub to not slow down on it's upstream connection, if you mix usb 1.1, usb 2.0 and usb 3.0 downstream.