Retouch images - size them - remove the background

I need to remove the background from 15 images and change it to one that I will give you, delete the logo and description in each image, resize the images 600x600 pixels with medium-high image quality, maximum weight for each image 40 kb. In alucne image insert the green wifi symbol.
The second part of the project includes 4 images.
Of these 4 images it is necessary to increase the quality of the image, eliminate the writings and logos, in two of these images there will also be to eliminate two temosifosi and replace them with two different ones.
For each of these 4 images create two different image sizes always with medium-high quality:

1) 600x600 pixels (which remains proportionate) in jpg format - medium high image quality - max image weight 50 Kb

2) 1200x480 (which remains proportioned) in jpg format - medium high image quality - max weight 80 Kb
I hope everything is quite understandable.