You can not direct migrate v8 to v10. First you need to migrate in v9 and then in v10.
Basically these are the steps :
a) First You need to download two openupgrade libraby,
b) Install openupgradelib.
1) Download openupgradelib from https://pypi.python.org/pypi/openupgradelib
2) Install with command : sudo python setup.py install
c) Run Automated Migration script
1) Go to specific path of openupgrade where you find 'migrate.py' file
2) python migrate.py --config=[your openerp.conf] --database=[your database] --run-migrations=[your migrations]
--config = v9 config file(in which version you want to migrate)
--database = database which we would like to migrate(installed database)
--run-migrations = version in which you would like to migration
d) 'migration.log' file is created for error tracking.
e) If any error occured while migration script is running, need to solve explicitly the problem(by psql) and run migration script again.
f) New database is created in v9 'databasename_migrated' with '_migrated'.
Let me know if any further query,