My phone is running out of space, and even when I delete someone my things, it is still low space
No, it will clear out the whole phone memory including contacts and other data but not the SD Card data. Before doing the factory reset, first save your data from phone memory and then go with the Format Factory procedure of your phone.
Here are some best tips to make space and increase memory:
1.) Move all downloaded apps to SD storage.
2.) Remove all unwanted apps and data.
3.) Clear out the cache from the phone. For this just go to settings>>apps and select app and you will get the clear cache option. (You have to do it for all applications installed in phone memory.)