If your trying to get the bassy "CHUG" like Mesa boogie rectifiers , its basically impossible. You can get a EQ pedal but the difference is minimal with a small amp. My recommendation, get a better practise amp cause you have to spend like $100 plus to get the EQ pedal and the difference is also minimal. Meaning you wont get the sound your looking for. Another way to get your sound Bassier is to get Mahogany bodied guitar.
If you want a good sounding practise amp i do have a few recommendations.
Randall V2XM
Orange Crush30
Tech21 Trademark 30
Vox VT30
Roland Cube30