For some reason the 7A isn't listed as part of the 7 series family on the MIUI download page. There looks to be a global 10.3.5.0 available which MIUI should find and install for you but you can do it manually by saving to local device and then do upgrade via settings -> update -> select zip from from local storage but you'll still have Xiaomi bloatware. Once your bootloader is unlocked you could use TWRP to wipe /dalvik /system /data and /cache then flash the newest rom and Magisk/SuperSU to give you root which should then give you the option to remove the Mi apps.
There are people on here who can help with the above (like replacing Recovery with TWRP) but do some research on the procedure as it can be quite daunting the first time you flash a phone as you can brick it.
There are people on here who can help with the above (like replacing Recovery with TWRP) but do some research on the procedure as it can be quite daunting the first time you flash a phone as you can brick it.