Depending on how they release updates you may not be able to. Try downloading and installing without deleting the previous version if it gives you the option to update an existing version then you should be fine. But if they released it as a separate app instead of a updated app then the only way to carry over your save is with a rooted device. Unfortunately android likes to hide its internal workings so unless the developer sets it up you can't normal get access to some app files. This unfortunately includes save files. It may be annoying but its better to stat new every update any ways it reduces the chances of errors. If it refuses to install it maybe because you don't have enough space android likes to keep a certain amount of space free for updates. So it may look like you have 1gb of space but android may only allow you to use 500mb of that.