Umbraco database tends to grow quite quickly especially when it's a high-traffic website. There are several thing you can do in order to reduce its size.

Shrink database log file

First of all, try shrinking the database log. To do that, in SQL Management tool, right click on the database, select Tasks -> Shrink -> Files. In the Shrink File window, change file type to Log and click on OK.

Shrink database

Tasks -> Shrink -> Database and click OK, if database is large, this may take several minutes. In terms of reducing the database size, this is probably the most effective way.

Empty Umbraco log table

Execute TRUNCATE umbracoLog to empty the database. TRUNCATE is quicker than DELETE and will reset the counter back to 0.