Many different ways. In no particular order
1) Use the quick selection tool to select the wall, create a hue saturation layer using the selection as a mask and move the hue slider
2) Use select color range to select the wall, then change as above
3) Eyedropper the wall, then choose image->adjustments->replace color
There are many other ways to do this, these are just a few. Some options work better than others depending on the contents of the picture.
To master PS requires hours (and in some cases years) of playing. Learning how to change to color of a wall is a good place to start playing.
EDIT: Do you mean LR or PS? The thread says lightroom, you say you own lightroom, but you also talk about PS. If you need instructions for LR, sorry, very little experience there.