[How do you change certain colours and text in a JPEG image?]

I play an online game and i come up with a good majority of media, however one guy who plays this game made some media and he has now stopped playing, I basically need to alter and make new versions of this media :

http://images43.fotki.com/v1382/photos/ ... nia-vi.jpg

There are different versions of this image, with different text names, and different colour backgrounds of the cross

Is there anyway to alter the colour of the cross without changing the colour of the whole image, and is there anyway to change the text near the top of the image?

Any help would be much appreciated

Thanks

[HOW TO INSTALL PLUGINS/General Plugin Troubleshooting Thread]

ok bassically im new to paint.net

and i want to download the plugin : conditional Hue/Saturation Adjustment

so ive downloaded the file to a folder on my computer, ive tried to extract it but it comes up with a message that it cannot be read :S

so anyway i tried instead moving the download straight to effects in my c drive and it isnt showing up when i load paint.net

can anyone suggest what i am doing wrong?

thankyou