Must upgrade to Android version 10/newer

Short answer: you probably can't.

Long answer: Android (like any mobile OS) has to be built for the particular model of device it is to run on. You cannot download a generic Android 10 and install it on any device. Normally the device manufacturer builds and tests updates and you download and install them from the device's Settings (exactly where the "System Updates" menu is will depend a little on manufacturer and version, but start by looking in the System settings or the menu items towards the end of the Settings). If there are no updates available that tells you that the manufacturer hasn't made one. If you are still on Android 6 there is basically no chance that there will be an official update to 10 or higher (many manufacturers of budget devices never produce updates at all).

If there is no official update available you can see whether there is a "custom ROM" based on a more recent version. This will involve unlocking the bootloader (if possible), installing a custom recovery (if someone has made one for that model) and using that to install the ROM (if someone has made one for this model). A good place to look for information on this is the xda-developers forum. But note, like official software community software (ROM and recovery) must also be built for the specific device: a ROM or recovery made for a different model will not work and will probably render your device unusable (using a recovery built for a different model is particularly risky). Even if you find something I'd advise also finding out how to reflash your device with stock software first, in case anything goes wrong.

However, you are asking for a big update: at least 4 major versions. Very few devices have custom ROM support that extends that long: most developers move on before then, and anyway it's often not possible, e.g. if one of the (old) components doesn't have a driver that's compatible with a newer android build that's game over. There have been a very small number of devices where an enthusiast community have worked very hard to update to newer versions, but the number that got from 6 to 10 is still small, and tablets were less popular for development than phones. So to be honest I think you will be very lucky if there is a suitable ROM for your device.