Learn Finnish: Tämä pyörätie uudistettaisiin kesällä. - This bike path would be renewed in the summer.

The dictionary form is uudistaa (to renew). A reliable trick to form the conditional passive is to take the past passive participle uudistettu (renewed) and replace the -tu ending with -taisiin. This gives you uudistettaisiin (would be renewed).

Why is the object tämä pyörätie in the basic nominative form instead of taking an object ending?

When a completely affected singular object is the target of a passive verb, it takes the basic nominative case (no ending) instead of the -n ending. If the sentence had an active subject like 'I would renew this bike path', you would need the -n ending and say tämän pyörätien.

Why does kesällä use the -llä ending here?

The adessive case (ending in -lla or -llä) is used to express 'in' or 'during' a certain season, time of day, or holiday. Because of this rule, kesä (summer) becomes kesällä (in the summer).

How does the verb uudistaa relate to the word for new?