docs(tests): improve upgrade tests README

diff --git a/docs/tests/upgrade-tests.md b/docs/tests/upgrade-tests.md
index 93da4856..b85e592f 100644
--- a/docs/tests/upgrade-tests.md
+++ b/docs/tests/upgrade-tests.md
@@ -1,8 +1,9 @@
 # Running Upgrade Tests
 
-1. As always, use uv environment:
+1. As always, use `nix-shell` + `uv` environment:
 
 ```sh
+nix-shell
 uv sync
 source .venv/bin/activate
 ```
@@ -15,7 +16,14 @@ tests/download_emulators.sh {model}
 
 For tropic-capable models, this also downloads tropic-enabled emulator variants into the same subfolder layout as on S3.
 
-3. And run the tests using pytest:
+3. Build the emulator for the model you want to test, use `DISABLE_TROPIC=0` for tropic-enabled models:
+
+```sh
+make -C core build_unix TREZOR_MODEL=T2T1
+make -C core build_unix TREZOR_MODEL=T3W1 DISABLE_TROPIC=0
+```
+
+4. And run the tests using pytest:
 
 ```sh
 pytest tests/upgrade_tests
@@ -23,8 +31,15 @@ pytest tests/upgrade_tests
 
 ----
 
-You can use `TREZOR_UPGRADE_TEST` environment variable if you would like to run core or legacy upgrade tests exclusively. This will run `core` only:
+You can use `TREZOR_UPGRADE_TEST` to limit the run to specific models.
+Accepted values are model internal names (`T1B1`, `T2T1`, `T3W1`), and they can be combined as a comma-separated list.
 
 ```sh
-TREZOR_UPGRADE_TEST="core" pytest tests/upgrade_tests
+TREZOR_UPGRADE_TEST="T2T1" pytest tests/upgrade_tests
+TREZOR_UPGRADE_TEST="T3W1" pytest tests/upgrade_tests
+TREZOR_UPGRADE_TEST="T1B1,T3W1" pytest tests/upgrade_tests
 ```
+
+If `TREZOR_UPGRADE_TEST` is not set, this command auto-selects targets based on locally available emulator builds.
+`T1B1` (legacy) runs when the local legacy emulator is available, and `T2T1`/`T3W1` (core) runs when the local core emulator is available.
+For local core builds, the suite detects the model from the build tree; if it cannot be determined, the run fails explicitly and you should set `TREZOR_UPGRADE_TEST` yourself.