Hi @alexanderucup
Here's the [https://downloadcenter.samsung.com/content/UM/201809/20180927163504404/SM-G570_G610_UM_SWA_Oreo_Eng_Rev.1.0_180927.pdf|user manual] for the phone.
Go to the ''My Files'' section on p.94 to see how to manage your files.
On p.48 there's a section dealing with ''uninstalling apps'' as well.
Also if you wish to increase the storage capacity of the phone, the phone supports micro SD cards with a capacity of up to 256GB.