Welcome to the community!
Which Huawei device do you have? Unfortunately, the L04 designation is not unique to any particular phone model. I believe that labelling relates to a particular region version for Huawei devices rather than the device model itself. For example, the Huawei Y6 (SCL-L04), Huawei P8 Lite (ALE-L04), and Huawei P30 (ELE-L04) all have a L04 version. In fact, I believe most Huawei models have a L04 version.
Whether or not you'd be able to upgrade to Android 6 would depend on whether that OS was made available for the device by Huawei.
Hope this helps 😀
It's a Huawei Y6. It isn't acutally written anywhere on the phone so it takes a little searching to find the model. Does that mean if the manufacturer didn't provide an update it is impossible to update the OS?
If the manufacture did not provide the update then it would not be possible to update officially.
That does not mean all is lost there is still a development community that sometimes continue to build a custom OS for devices, you can check forums like XDA Developers.
Flashing a custom ROM is not something you should do if you do not have any knowledge of if as it could brick your phone.