First sort out the guttering so it does not leak as this is what has likely caused this in the first place.
When it's absolutely peeing it down, get yer coat on and go out and have a look at it.
Then powerwash what you can off, if the result is acceptable then all is fine.
If not then consider painting it but this is likely going to require the whole house doing so it looks right.
Although looking at the rest of the front wall, it all looks like it could do with washing off.
Don’t pressure wash it , you’ll strip the surface off the render. most black marks in k-rend are fungal. you’ll need dedicated cleaner . K-rend recommend soft wash render cleaning products and techniques.
check their website.
I may be wrong, but the doorsteps and gravel on the RHS, may cause issues with their proximity to the DPC?
Splashback from this area also looks to be staining the render.
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