Squeek needs to lose a little weight, how much to feed?

[CJinCA]

at the last vet visit, Squeek was almost 3lbs up from the previous year, right after we adopted her and Lickorish. Lickorish was up about 1lb (squeek always finishes the food Lickorish doesn't eat). I'm pretty sure it has to do with the excessive treats my hubby and I have been giving them. We feed mostly grain-free canned, a variety of brands including Wellness, natural Balance, Merricks.

so if she's 13.5 lbs now, how much should I feed to get her back down to her previous 10.5 lbs? She is spayed and indoor only, fairly active. Most cans we have say feed 1 can / day per 7 lbs of weight, or something close to that, but how much should I feed for her to lose weight?