How can I lower the brightness of my screen in my Dell 1525 lapto

Sometimes the brightness is on the arrow keys hit the Fn or function key and press down on the arrow to dim the light or press up on the arrow key to increase brightness

Easy one, press the function button (bottom right) use up and down keys to get to brightness, push function again and use up and down arrows to adjust when set click function to exit

Good news!
Here's how you adjust the brightness settingon the Dell Inspiron 1525 Laptop monitor.
Hope this helps you!
CBR2009

<Fn> and up-arrow key Increases brightness on an integrated display.
<Fn> and down-arrow key Decreases brightness on the integrated display only (not on an external monitor).

PLEASE NOTE: Rebooting the computer returns the ambient light sensor to it’s prior setting
(either enabled or disabled).

Other brightness settings:
Keyboard/ Touch Pad brightness settings — Press <Fn> and the right-arrow key to toggle between the three lighting states (in the given order).
The three lighting states are:
1 full keyboard/touch pad brightness.
2 half keyboard/touch pad brightness.
3 no lighting.

While holding the Fn (Function) Button on the lower left corner of your keyboard(near CTRL key) press the birghtness buttion on the keyboard (should be one of the buttons on F1-F12 row and the brigness icon will be blue).

You can use the Fn button to access al the function that are colored blue on your keyoboards F1-F12 keys

That all depends on what "Screen" you have.... if it is a laptop there is usually a function key on the lower left which combines with a color coded key on your keyboard to control brightness.

If this is an LCD there is usually a menu which can be gotten to by buttons on the front where brightness can be controlled.

Finally if this is an old CRT, there are either buttons or dials (if analog) on the front to control this.

Hope this helps.