Hi Joaquin...since your geraniums' leaves have a ring, the more sun the better. The ring will darken with sun, otherwise, if in shade, it'll revert to green.
Was your geranium in or outdoors when you bought it? It may need light adapting, but since its leaves are yellow, it sounds more like an overwatering problem..Geraniums do not like wet feet. Water thoroughly, then let soil dry before adding more.
Geraniums need well-draining soil. If/when you repot use a Cactus/succulent soil, and amend if it's still too heavy. I use Succulent soi and add Builder's Sand (bought at HD) and Perlite. If you don't want to bother with sand, just use the Perlite. Also, pots should have drainage holes. Otherwise, water will build up on the bottom pot and cause root rot. Treat Geraniums as you would a succulent plant. Good luck, Toni