Help to upgrade parts

So I brought an old pc with out the knowledge of pc parts selling it hasn’t work but me and my brother want to up grade it and the last owner said it’s possible. We upgraded it over time so I would appreciate listening to of parts that we can update to.

(I know they old that’s why we want to upgrade) Specs are

I5 4460 GtX 960 16GB DDR3 Ram 400w power supply 128GB SSD 1TB HDD

We would like to upgraded all of it including the power supply & motherboard but we not sure what type of motherboard but we want to upgrade so it can support a better I part

what we would like the pc to do is have windows 11 gaming streaming/recording, being good at multitasking and editing

Any help would be appreciated again I know it’s an old pc but selling it hasn’t work so we decided to just upgrade a bit at a time but not sure where to start so thought I would ask

Thanks in advance ☺️