Open the GIF in Photoshop CS5, CS6 or Creative Cloud versions If not already open, open the Animation window by selecting Window>Timeline, or Window>Animation Also, make sure the Layers window is open by selecting Window>Layers
01. Adjustment layers
In the Layers window, select the top most layer and use the 'Create new adjustment layer' icon to add a new adjustment layer.
Select the type of adjustment layer to use. Any changes to the adjustment layer will affect all the frames and layers below it.
Play around with different types of adjustments to get the desired effect. This is a great option for changing colors and contrast. When you're ready to save, go to 'Save for Web and Devices' from the File menu. In Photoshop CC, it's under File>Export. Select GIF, and the desired number of colors. Be sure to check the Transparency, Matte, and Animation Options at the bottom of the dialog. Click 'Save' and save the file as a new name.