Is it possible to increase price of an App?
You can set and change your price at any time. You can set price changes immediately, or scheduled ahead of time.

You can choose which price from a range of tiers provided by Apple.
eg. 99c, 1.99, 4.99, etc.

You can't yourself choose 49c or $2.68, or any arbitrary value.

See:

Changing Product Pricing

Scheduling Price Tier Changes

Pricing Tier Matrix