Very silly doubt

hello profis…
i am having one small doubt…it looks silly for you all…but i dont know…how to do…:frowning:

1 . I download one pic in stockphotos…i like to reduce the size without loosing the quality?..how can i reduce without losing quality??
i tried using paint…real draw pro …corel draw…but i am not getting the same clarity…and quality…
profis and gurus…please help me with ur suggestions…

cheers
Goodboy