It doesn't look too bad.
The sides of your oven ( the grey matt material) is self cleaning and should not be touched.
There may be a heating element in the roof of the oven- don't touch that either.
So all you have to do is the oven door, the floor of the oven, and the racks.
As other have said either put the racks in the dishwasher ( any residual muck will come off easily with a light scrub if you tackle it as soon as you remove it from the dishwasher.
If no dishwasher then buy a cheap kit- I have tried many and the pound shop ones are just as effective.
They come with a big bag and you put the shelves inside and pour in the solution- leaves for hours or overnight. ( I do this outside on a patch of gravel)
The floor needs to be lightly cleaned to get rid of debris and use the spray or solution- again leave for some time.
The door may need a second application as the solution will drip off and dry quite quickly on a vertical surface.
If you don't scrub straight away and allow the stuff to dry again then you will be back to square one.
You will probably need a second application.
Do make sure pets and children are kept away, wear gloves, the chemicals can burn skin.
Also protect your floor in front of your oven before you start cleaning, I use an opened up black bin liner and newspaper.
And just another point- don't store baking ware in your oven, I see you have some in there.
If you subject your trays to contant heating it will limit their lifespan, cause them to warp, make them more prone to sticking, making them more difficult to clean.
Good luck!