Hi Darohan,
I personally find replacing just the screen is far simpler than replacing the screen and frame, although you do have to be more careful - especially with OLED displays.
On most android phones you just need to heat up the screen with a heat gun, hairdryer, heat plate or something similar to soften the adhesive until you can insert a pry tool under the display to remove it. However as in your case the display has already come detached, you can completely skip this step : )
From there, you can just apply new liquid adhesive such as E8000 to glue the new display in place.
Hope this helps, let me know if you have any further questions : )